Automotive Calculation Lab

Device: Detecting…

Interactive automotive calculations for speed, tire revolutions, gearing, unit conversion, piston compression and rotary/Wankel compression, including piston and rotary measurement procedures and worksheets, with automatic PC/mobile detection and a full automotive engineering toolkit.

Automotive engineering calculations in one workspace

Calculate vehicle speed, RPM, tire geometry, gearing, engine displacement, compression ratio, power, torque, airflow, fuel requirements and more. Use the Advanced Workspace to connect these calculations into a vehicle model.

Speed & RPM guide Tire size guide Displacement guide Compression guide Engineering guides

Vehicle Speed / RPM

Switching Metric / English converts the actual tire-diameter number. Gear ratio and RPM remain unchanged.

Engine RPM

Tire diameter (in)

Transmission gear ratio

Final-drive ratio

Driveline slip (%)

Calculated speed

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mph

mph = RPM × tire diameter(in) × π ÷ (gear × final drive × 1056) × (1 − slip/100)

Tire revolutions per mile

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Theoretical circumference-based value

Wheel RPM

—

Engine RPM ÷ (transmission ratio × final drive ratio)

Piston-engine Compression Ratio

Swept volume per cylinder

Clearance volume

Compression ratio

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Geometric ratio :1

CR = (swept volume + clearance volume) ÷ clearance volume

How to Measure a Piston Engine's Compression Ratio

For an actual engine, compression ratio is determined from the measured swept volume and the measured clearance volume. The goal is to account for the piston, cylinder head, gasket, deck height, and any other volumes that remain above the piston at top dead center (TDC).

1Measure the bore

Measure the actual cylinder bore diameter with a bore gauge or suitable precision measuring tool.
If the engine is apart, measure at several heights and orientations to identify taper or out-of-round.
Use the actual finished bore, not just the nominal advertised bore.

2Measure the stroke

Measure crankshaft travel from bottom dead center (BDC) to top dead center (TDC).
If the crankshaft is stock, the manufacturer's stroke specification can be used as a reference.
For a modified engine, verify the actual stroke whenever practical.

3Measure combustion-chamber volume

With the cylinder head removed, position the head so the chamber can be filled and the valves are closed.
Use a calibrated burette or graduated measuring device to fill the chamber.
Record the liquid volume required to fill the chamber without trapped air.

4Measure head-gasket volume

Measure the gasket's compressed thickness if possible.
Measure the gasket bore diameter.
Calculate gasket volume as the area of the gasket opening multiplied by compressed thickness.

5Measure deck clearance

Bring the piston to true TDC.
Measure how far the piston is below or above the deck.
For a piston below the deck, calculate the volume between the piston crown and deck surface.
If the piston crown is domed or dished, measure its volume separately rather than treating it as a flat piston.

6Account for piston-crown volume

A dish adds clearance volume.
A dome displaces volume and therefore reduces clearance volume.
Use a measured piston volume when available rather than relying only on a catalog specification.

V_swept = (π ÷ 4) × Bore² × Stroke
V_clearance = chamber + gasket + deck + piston-crown effects + other retained volumes
CR = (V_swept + V_clearance) ÷ V_clearance

Important: compression ratio is normally calculated per cylinder. Do not multiply the compression ratio by the number of cylinders. Cylinder count is needed when calculating total engine displacement.

Piston Engine Measurement Worksheet

Manufacturer / engine model

Measured bore diameter (mm)

Measured stroke (mm)

Combustion chamber volume (cc)

Head gasket volume (cc)

Deck-clearance volume (cc)

Piston-crown volume effect (cc)

Other retained clearance volume (cc)

Common source of error: using the nominal chamber volume, gasket thickness, or piston specification without accounting for the actual assembled engine. Deck height, compressed gasket thickness, piston dish/dome, machining, and chamber work can materially change the final result.

Worksheet swept volume

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Worksheet clearance volume

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Worksheet compression ratio

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Rotary / Wankel Compression Ratio

Measure the same working chamber at its minimum and maximum volumes. This direct-volume method is preferred for rebuilt or modified engines.

Maximum chamber volume (Vmax)

Minimum chamber volume (Vmin)

Compression ratio

—

Geometric ratio :1

Swept chamber volume (Vsw)

—

Vmax − Vmin

Measurement check

—

Vmax must be greater than Vmin

Vsw = Vmax − Vmin
CR = Vmax ÷ Vmin = (Vsw + Vmin) ÷ Vmin

Important: rotor count is used when documenting or calculating total engine displacement, but it is not multiplied into the geometric compression ratio.

How to Measure a Rotary Engine's Compression Ratio

Use this procedure when you need the compression ratio of an actual engine, especially a rebuilt or modified engine. Record all measurements in cc for consistency.

1Prepare the engine

Remove the spark plug for the chamber being measured.
Clean the plug area so debris cannot enter the engine.
Inspect for deposits, machining, porting, and seal changes.

2Position for Vmin

Rotate the engine until the selected working chamber is at its smallest volume.
Use the actual housing geometry; do not assume a generic rotor position.
Prevent the rotor from moving during the measurement.

3Seal the chamber

Seal openings that would allow measurement fluid to escape.
Use appropriate plugs, fixtures, or non-damaging seals.
Make sure the setup does not add unintended volume.

4Measure Vmin

Use a calibrated burette or precision graduated syringe.
Fill the chamber slowly through the spark-plug opening.
Eliminate trapped air bubbles and record the fluid volume.

5Position for Vmax

Rotate the engine until the same working chamber reaches maximum volume.
Keep the measurement method and sealing arrangement consistent.

6Measure Vmax

Fill the chamber again with the calibrated measuring device.
Remove trapped air and record the total volume.
Repeat measurements if the readings are inconsistent.

Example: If Vmin = 50 cc and Vmax = 700 cc, then Vsw = 700 − 50 = 650 cc and CR = 700 ÷ 50 = 14.0:1.

Rotary Measurement Worksheet

Manufacturer / engine model

Number of rotors

Measurement fluid

Measuring device

Vmin measurement #1 (cc)

Vmin measurement #2 (cc)

Vmax measurement #1 (cc)

Vmax measurement #2 (cc)

Notes / modifications

Measurement considerations: spark-plug recesses, combustion-chamber recesses, port geometry, apex-seal position, gasket thickness, rotor/housing machining, carbon deposits, leakage, and other engine modifications can affect the measured volume. Be consistent about what is included in both Vmin and Vmax.

Quick Reference Engineering Toolbox

Expanded calculators for engine building, gearing, tires, forced induction, vehicle performance, suspension, braking, electrical systems, and saved build sheets. Enter your measurements and the results update live.

Advanced Build & Engineering Workspace: Use the dedicated Advanced Workspace tab for interconnected build workflows, engineering labs, vehicle comparisons, and saved-build tools.

Engine Displacement

Bore (mm)

Stroke (mm)

Cylinders

Total displacement

—

Total displacement

—

V = π/4 × bore² × stroke × cylinders

Power & Torque

Torque (lb-ft)

Horsepower

RPM

HP from torque

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Torque from HP

—

HP = torque(lb-ft) × RPM ÷ 5,252

Airflow / VE

Displacement (CID)

RPM

VE (%)

—

Estimated naturally aspirated airflow requirement.

CFM = CID × RPM × VE ÷ 3456

Fuel Injector Sizing

Target HP

BSFC (lb/hp-hr)

Injector count

Max duty cycle (%)

Required injector flow

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Approx. cc/min (gasoline)

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cc/min conversion is an approximate gasoline conversion; fuel density varies.

Gear / Final Drive

Target RPM

Target speed (mph)

Tire diameter (in)

Required overall ratio

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Final drive with entered gear

—

Transmission gear ratio

Overall ratio = RPM × tire diameter ÷ (mph × 1056 × π)

Shift RPM

Current RPM

Current gear

Next gear

Post-shift RPM

—

RPM drop

—

RPM₂ = RPM₁ × next gear ratio ÷ current gear ratio

Tire Size Calculator

Width (mm)

Aspect (%)

Wheel (in)

Sidewall

—

Diameter

—

Rev/mile

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Tire Comparison

Tire A (e.g. 245/45R17)

Tire B (e.g. 255/40R18)

Metric	Tire A	Tire B	Difference
Diameter	—	—	—
Circumference	—	—	—
Rev/mile	—	—	—

Speedometer Error

Indicated speed (mph)

Original tire diameter (in)

New tire diameter (in)

Actual speed

—

Error

—

Boost / Pressure Ratio

Boost (psi)

Atmospheric pressure (psi)

Pressure ratio

—

Absolute manifold pressure

—

PR = (boost + atmospheric pressure) ÷ atmospheric pressure

Forced-Induction Airflow

Displacement (CID)

RPM

VE (%)

Boost (psi)

Atmospheric (psi)

—

Simplified idealized airflow estimate; temperature, intercooling and compressor efficiency are not included.

Wheel Torque / Drivetrain Loss

Engine torque (lb-ft)

Gear ratio

Final drive

Drivetrain efficiency (%)

Wheel torque

—

Wheel torque ≈ engine torque × gear × final drive × efficiency

0–60 / Quarter-Mile Estimate

Vehicle weight (lb)

Wheel HP

Traction factor

Estimated 0–60 mph

—

Estimated 1/4 mile

—

Performance estimates are simplified planning tools, not predictions. Traction, gearing, launch, aero, surface and driver technique can materially change real results.

Braking / Stopping Distance

Speed (mph)

Tire/road friction coefficient

Braking distance

—

Stopping time

—

d = v² ÷ (2 μ g)

Weight Distribution / CG

Front axle weight (lb)

Rear axle weight (lb)

Wheelbase (in)

CG height (in)

Front / rear distribution

—

Static axle balance

—

Suspension / Wheel Rate

Spring rate (lb/in)

Motion ratio

Corner weight (lb)

Wheel rate

—

Approx. ride frequency

—

Wheel rate = spring rate × motion ratio²

Aerodynamic / Rolling Power

Speed (mph)

Frontal area (ft²)

Rolling resistance

Weight (lb)

Air density (slug/ft³)

Aero power

—

Rolling power

—

Automotive Electrical

Voltage (V)

Current (A)

Resistance (Ω)

Power

—

V from I × R

—

I from V ÷ R

—

V = I × R P = V × I

Voltage Drop

Current (A)

Total resistance (Ω)

Voltage drop

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Power lost

—

Alternator / Battery Load

Alternator rating (A)

Electrical load (A)

Desired reserve (%)

Recommended minimum alternator

—

Reserve at rated output

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Vehicle / Engine Build Sheet

Save a build profile in this browser and use its core values across the toolkit.

Build name

Bore (mm)

Stroke (mm)

Cylinders

Engine HP

Engine torque (lb-ft)

Vehicle weight (lb)

Tire diameter (in)

Final drive

Redline (RPM)

Top gear ratio

Notes

Saved builds

Build displacement

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No build saved yet.

Advanced Build & Engineering Workspace

Interconnected tools, transparent math, engineering calculators, build comparison and vehicle profiles.

Local-only workspace

Engineering Intelligence Connected analysis across the calculators and your current build.

Change Impact Engine

Change a tire, final drive, weight or power value and see the system-level effect at a selected road speed.

Proposed tire diameter (in)

Proposed final drive

Proposed weight (lb)

Proposed wheel HP

Road speed (mph)

Top/selected gear

Calculation Inspector 2.0

Every result is classified and shows the formula, substitution, input provenance, assumptions, unit basis and supporting guide where available.

Advanced Gearbox Simulator

Six-speed table with redline speed and post-shift RPM. Uses the shared calculation library.

Tire diameter (in)

Final drive

Redline RPM

Current RPM

Current gear

1st

2nd

3rd

4th

5th

6th

Measured vs. Calculated

Use real measurements when available; the system preserves the nominal calculation separately.

Calculated diameter (in)

Measured diameter (in)

Use measured values for physical-vehicle analysis when tire construction, load, pressure or growth makes the nominal dimension insufficient.

Shared Calculation Library

The same core functions drive speed, RPM, tire, displacement and power calculations, preventing different tools from silently using different formulas.

Build Comparison — System Impact

Build A

Build B

Vehicle Engineering Intelligence

A persistent vehicle model connecting calculations, measurements, assumptions, scenarios and engineering explanations.

CalculatedPlanning calculation

Vehicle Digital Twin

Engine

Transmission

Final drive

Tire diameter (in)

Vehicle weight (lb)

Wheel HP

Input Provenance & Confidence

Every important result can be identified as exact geometry, calculated from nominal specifications, estimated from assumptions, measured by the user, or manufacturer-supplied.

What-If Scenario Lab

Scenario A

Tire diameter

Final drive

Scenario B

Tire diameter

Final drive

Engine RPM

Transmission gear

Road speed

Sensitivity Analysis

Engineering Reference & Formula Provenance

Calculation Validation

Result Classification

EXACT

Direct mathematical relationship from stated inputs.

CALCULATED

Derived from nominal specifications or standardized assumptions.

ESTIMATED

Empirical or simplified model; actual results can differ.

Guided Measurement Worksheet

Rollout distance for 10 revolutions (in)

Loaded tire radius (in)

Tire pressure (psi)

Procedure: mark the tire, roll exactly 10 revolutions under normal load, measure the distance, divide by 10, and preserve pressure/load conditions in the note.

Engineering Notes

Engineering Learning Path

Garage / Builder / Engineer

Explain This Number

Planning & Safety Verification

These tools are for planning and analysis. Brake, suspension, wheel, structural and other safety-critical results should be verified against component specifications, applicable standards, and qualified engineering practice before fabrication or operation.

Automotive Engineering Graph

Engine
RPM / Torque→Transmission
Gear ratio→Final Drive
Multiplication→Tire
Effective radius→Vehicle
Speed / Force

1. Tire Size Parser & Visualizer

Tire A

Tire B

2. Calculation Inspector

Every advanced result can expose inputs, formula, substitution, assumptions and result.

Run a calculation to inspect the math.

3. Gearbox Simulator

Redline RPM

Tire diameter (in)

Final drive

RPM sample 1

RPM sample 2

RPM sample 3

1st

2nd

3rd

4th

5th

6th

4. Calculator Chaining

Tire → Speed
Parsed tire diameter can populate speed/gear tools.

Displacement → Airflow
Engine displacement can populate the airflow tool.

Build → Everything
Use saved build values across relevant calculators.

Mean Piston Speed

Stroke (in)RPM

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MPS = 2 × stroke × RPM ÷ 12, in/min converted to ft/min.

Rod / Stroke Ratio

Rod length (in)Stroke (in)

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BMEP

Torque (lb-ft)Displacement (CID)

—

Deck Height / Piston Position

Block deck height (in)Rod length (in)Stroke (in)Compression height (in)

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Dynamic Compression

Static CREffective stroke fraction (0–1)

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Simplified geometric estimate based on effective swept-stroke fraction; use a full valve-event model for precision.

Valve Area

Valve diameter (in)Valve count

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AFR ↔ Lambda

Gasoline AFR referenceValue

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Injector Pulse Width

Injector flow (lb/hr)Fuel flow required (lb/hr)InjectorsEngine RPM

—

Simplified pulse-width estimate; dead time and operating pressure are not included.

Fuel Pump Sizing

Engine HPBSFCFuel density (lb/gal)Safety factor (%)

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Fuel Flow / BSFC

HPFuel flow (lb/hr)

—

Octane Blend

Fuel A octaneFuel B octaneTarget octane

—

Linear volume blend approximation; real fuel behavior can differ.

E85 Blend

Gasoline ethanol %Target ethanol %Total blend volume

—

Converter Slip

Engine RPMCalculated turbine/wheel RPM

—

Driveshaft RPM

Engine RPMTransmission ratioFinal drive

—

Speedometer Gear

Current driven gear teethCurrent drive gear teethNew tire diameter (in)Old tire diameter (in)

—

Wheel Offset / Backspacing

Wheel width (in)

Offset (mm)

—

Wheel Comparison

Old width (in)Old offset (mm)

New width (in)New offset (mm)

Charge-Air Temperature

Ambient °FCompressor outlet °FIntercooler effectiveness %

—

Compressor Flow Estimate

Engine CIDRPMVE %Pressure ratio

—

Boosted Compression

Static CRBoost psiAtmospheric psi

—

Pressure-ratio-based comparison, not a combustion-model prediction.

Vehicle Performance Dashboard

Weight (lb)

Wheel HP

Traction factor

—

The acceleration estimate is intentionally labeled as an estimate, not a prediction.

Weight / CG

Front axle lb

Rear axle lb

Wheelbase in

CG height in

—

Suspension

Spring rate lb/inMotion ratioCorner weight lb

—

Aero / Rolling Resistance

Speed mph

Frontal area ft²

Crr

Weight lb

Air density slug/ft³

—

Vehicle Preset Library

Create your own stock/build presets locally. The app does not invent factory specifications.

Preset name

Saved presets

For factory data, enter verified specifications from your service manual/manufacturer documentation.

Build A vs Build B

Build A

Build B

Change-Impact Analysis

Compare the current Build Sheet with a proposed set of tire, gearing, weight and power changes.

New tire diameter (in)

New final drive

New weight (lb)

New wheel HP

Reference speed (mph)

Reference gear

Build Tools

Build data remains in your browser unless you export/share it.

Core Automotive Formulas

Engine displacement

V = π/4 × bore² × stroke × cylinder count

Injector sizing

Injector lb/hr = HP × BSFC ÷ (injector count × duty cycle)

Natural-aspiration airflow

CFM = CID × RPM × VE ÷ 3456

Pressure ratio

PR = (boost + atmospheric pressure) ÷ atmospheric pressure

Shift RPM

RPM₂ = RPM₁ × next gear ratio ÷ current gear ratio

Wheel rate

Wheel rate = spring rate × motion ratio²

Braking distance

d = v² ÷ (2 × μ × g)

Electrical power

P = V × I V = I × R

Vehicle speed

mph = RPM × tire diameter(in) × π ÷ (gear × final drive × 1056)

Engine RPM

RPM = mph × gear × final drive × 1056 ÷ (tire diameter(in) × π)

Tire revolutions per mile

rev/mi = 63,360 ÷ (π × tire diameter in)

Piston displacement

V = π/4 × bore² × stroke × cylinder count

Piston compression ratio

CR = (swept volume + clearance volume) ÷ clearance volume

Rotary compression ratio

Vsw = Vmax − Vmin
CR = Vmax ÷ Vmin = (Vsw + Vmin) ÷ Vmin

Horsepower from torque

hp = torque(lb-ft) × RPM ÷ 5,252

Wheel torque

wheel torque ≈ engine torque × gear × final drive × drivetrain efficiency

Automotive engineering calculations in one workspace

Vehicle Speed / RPM

Live Unit Converter

Piston-engine Compression Ratio

How to Measure a Piston Engine's Compression Ratio

1Measure the bore

2Measure the stroke

3Measure combustion-chamber volume

4Measure head-gasket volume

5Measure deck clearance

6Account for piston-crown volume

Piston Engine Measurement Worksheet

Rotary / Wankel Compression Ratio

How to Measure a Rotary Engine's Compression Ratio

1Prepare the engine

2Position for Vmin

3Seal the chamber

4Measure Vmin

5Position for Vmax

6Measure Vmax

Rotary Measurement Worksheet

Quick Reference Engineering Toolbox

Engine Displacement

Power & Torque

Airflow / VE

Fuel Injector Sizing

Gear / Final Drive

Shift RPM

Tire Size Calculator

Tire Comparison

Speedometer Error

Boost / Pressure Ratio

Forced-Induction Airflow

Wheel Torque / Drivetrain Loss

0–60 / Quarter-Mile Estimate

Braking / Stopping Distance

Weight Distribution / CG

Suspension / Wheel Rate

Aerodynamic / Rolling Power

Automotive Electrical

Voltage Drop

Alternator / Battery Load

Vehicle / Engine Build Sheet

Advanced Build & Engineering Workspace

Change Impact Engine

Calculation Inspector 2.0

Advanced Gearbox Simulator

Measured vs. Calculated

Shared Calculation Library

Build Comparison — System Impact

Vehicle Engineering Intelligence

Vehicle Digital Twin

Input Provenance & Confidence

What-If Scenario Lab

Sensitivity Analysis

Engineering Reference & Formula Provenance

Calculation Validation

Result Classification

Guided Measurement Worksheet

Engineering Notes

Engineering Learning Path

Garage / Builder / Engineer

Explain This Number

Planning & Safety Verification

Automotive Engineering Graph

1. Tire Size Parser & Visualizer

2. Calculation Inspector

3. Gearbox Simulator

4. Calculator Chaining

Mean Piston Speed

Rod / Stroke Ratio

BMEP

Deck Height / Piston Position

Dynamic Compression

Valve Area

AFR ↔ Lambda

Injector Pulse Width

Fuel Pump Sizing

Fuel Flow / BSFC

Octane Blend