Engine Displacement Calculator
Engine displacement in cc, litres and cubic inches from the bore, stroke and number of cylinders, and the static compression ratio from the clearance volume or from the chamber, gasket, deck and piston volumes.
Result…
How it's calculated
Swept volume per cylinder = π ÷ 4 × bore² × stroke Displacement = swept volume × cylinders · 1 in³ = 16.387064 cc (exact) · 1 L = 1000 cc Clearance volume = chamber + π ÷ 4 × gasket bore² × gasket thickness + π ÷ 4 × bore² × deck clearance + piston volume Compression ratio = (swept volume + clearance volume) ÷ clearance volume
Each cylinder sweeps a cylinder of air whose diameter is the bore and whose height is the stroke, so its swept volume is π ÷ 4 × bore² × stroke; the engine's displacement is that times the number of cylinders. The static compression ratio compares the volume above the piston at the bottom of its stroke (swept plus clearance) with the volume left at the top (the clearance volume). The clearance volume is the head's combustion chamber plus the gasket, the gap between the piston and the deck, and any dish in the piston, less any dome.
Your numbers, step by step
About the Engine Displacement calculator
This engine displacement calculator finds an engine's capacity from its bore, stroke and number of cylinders, in cubic centimetres, litres and cubic inches. Each cylinder sweeps a volume of π ÷ 4 × bore² × stroke, and the engine's displacement is that times the cylinders. Enter the bore and stroke in millimetres or inches. It also works out the static compression ratio, either from a clearance volume you already know or from its parts: the combustion chamber in the head, the head gasket, the gap between the piston and the deck, and any dish or dome in the piston. Engine builders use it to check a rebore, a stroker crank or a gasket change before buying parts, and the working shows each volume so you can see which part moves the ratio most.
How to use it
- Pick the “Units” and enter the “Bore”, the “Stroke” and the number of “Cylinders”.
- Under “Compression ratio”, choose “Skip”, “From clearance volume” or “From chamber, gasket, deck and piston”.
- For the parts, enter the “Combustion chamber volume”, “Head gasket bore”, “Compressed gasket thickness” and “Deck clearance”.
- Enter the “Piston volume”: positive for a dish or valve reliefs, negative for a dome.
- Read the displacement, the litres and cubic inches, and the compression ratio.
Worked example
A four-cylinder engine with an 86 mm bore and 86 mm stroke. Each cylinder sweeps 0.785398 × 86² × 86 = 499,557 mm³ = 499.56 cc, so the engine is 499.56 × 4 = 1,998.2 cc, or 2.0 L and 121.94 in³. With a 50 cc chamber, an 88 mm by 1 mm gasket (6.08 cc), 0.2 mm of deck clearance (1.16 cc) and a 5 cc dish, the clearance volume is 62.24 cc, and the compression ratio is (499.56 + 62.24) ÷ 62.24 = 9.03 : 1.
Updated
Questions people ask
How do I calculate engine displacement from bore and stroke?
Multiply π ÷ 4 by the bore squared and by the stroke, then by the number of cylinders. With millimetres, divide the answer by 1,000 for cubic centimetres.
What is the formula for compression ratio?
Compression ratio = (swept volume + clearance volume) ÷ clearance volume, as set out in the compression ratio article. The clearance volume is the space left above the piston at top dead centre.
How do I convert cc to cubic inches?
Divide by 16.387064, the exact number of cubic centimetres in a cubic inch. A 5,733 cc engine is 349.8 in³.
How much does a thinner head gasket raise compression?
It shrinks the clearance volume by π ÷ 4 × gasket bore² × the change in thickness. Try both thicknesses here and compare the ratios.
Is a dome entered as a positive or negative piston volume?
A dome takes up space above the deck, so it is negative; a dish or valve reliefs add space, so they are positive. Mixing these up is a common mistake that swings the ratio a long way.
What does the static compression ratio not tell me?
It ignores valve timing, so the pressure while running is lower than the static ratio suggests. For a build that must run on a given fuel, check with an engine builder; the horsepower and torque calculator helps with the power side.