Engine Displacement Calculator
Calculate Bore, Stroke, Cylinders or Displacement.
How to Use This Engine Displacement Calculator
Most online tools only allow you to calculate the final displacement. We designed this tool to be more versatile for engine builders and machinists. It works as a Solver, meaning you can enter any three known values to find the fourth.
- Calculate Displacement: Enter your Bore, Stroke, and Cylinder count to see the total engine size.
- Calculate Required Bore: If you have a target displacement (e.g., a specific racing class limit like 5.0L) and a fixed crankshaft stroke, leave the “Bore” field empty. The tool will tell you exactly how big you need to bore the cylinders.
- Calculate Stroke: If you are stroking an engine and want to know what crankshaft throw is required to hit a specific cubic inch target with your current block, leave “Stroke” empty.
Note on Units: You can mix and match units. For example, you can input Bore in inches and Stroke in millimeters, and request the result in Liters. The calculator handles the conversion automatically.
The Math Behind the Engine
Engine displacement is simply the total volume of air swept by all pistons during one full cycle. While it feels like a measure of “power,” it is technically a measure of “breathing capacity.” The larger the volume, the more air-fuel mixture the engine can ingest, and theoretically, the more power it can produce.
The standard formula used by this calculator is:
Displacement = (π ÷ 4) × Bore² × Stroke × Number of Cylinders
Why do we use (π ÷ 4)?
You might remember high school geometry using π × r² (radius squared). In the automotive world, we almost never measure the radius of a piston; we measure the diameter (Bore). Using Bore² × 0.7854 (which is π/4) allows you to plug in the caliper measurement directly without dividing by two first.
Bore vs. Stroke: Understanding Engine Character
Two engines can have the exact same displacement but behave completely differently depending on how they achieve that volume. This is often referred to as the engine’s “geometry.”
1. Oversquare (Short Stroke)
- Configuration: The Bore is larger than the Stroke.
- Characteristics: These engines love to rev. Because the piston doesn’t have to travel as far up and down (shorter stroke), there is less stress on the connecting rods at high RPMs. You also have room for larger valves in the wider cylinder head.
- Typical Use: Formula 1, high-performance motorcycles, and sports cars like the Ferrari V8.
2. Undersquare (Long Stroke)
- Configuration: The Stroke is longer than the Bore.
- Characteristics: These engines produce massive low-end torque. The longer lever arm on the crankshaft (the throw) creates more twisting force. However, they are generally limited to lower RPMs because the piston speed becomes dangerously high.
- Typical Use: Trucks, diesel engines, and cruisers (like Harley-Davidson).
3. Square
- Configuration: Bore and Stroke are roughly equal.
- Characteristics: This offers a balance between torque and horsepower reliability. Many production engines aim for this middle ground to provide good driveability.
Displacement vs. Compression
It is important not to confuse Displacement with Compression Ratio, though they are related.
- Displacement is the volume of the cylinder swept by the piston (from Bottom Dead Center to Top Dead Center).
- Compression Ratio is the relationship between the swept volume and the combustion chamber volume (the space left when the piston is at the very top).
Boring out an engine increases displacement, which usually increases the compression ratio slightly because you are squeezing a larger volume of air into the same cylinder head chamber (unless you also change the pistons).
Quick Unit Reference
When sourcing parts or reading spec sheets, you will often need to convert between Imperial and Metric standards. Here are the most common conversion factors this calculator uses:
- 1 Liter (L) = 1,000 Cubic Centimeters (cc)
- 1 Liter (L) ≈ 61.02 Cubic Inches (ci)
- 1 Cubic Inch (ci) ≈ 16.39 Cubic Centimeters (cc)
Example: The famous “5.0 Liter” Ford Mustang engine is approximately 302 cubic inches. The “350 Small Block” Chevy is approximately 5.7 Liters.
FAQs
Q1. Does boring an engine 0.030″ over make a big difference?
A: On a standard V8, boring the cylinders 0.030 inches over (usually for a rebuild) typically adds only 5 to 8 cubic inches to the total displacement. While this won’t result in massive horsepower gains on its own, it restores the cylinder seal, which restores lost power.
Q2. Why is my calculation slightly different from the manufacturer’s spec?
A: Manufacturers often round their numbers for marketing. A “5.0L” engine might actually be 4,942cc or 4,988cc. Additionally, they sometimes round the bore/stroke numbers in brochures. This calculator gives you the exact mathematical volume based on your precise inputs.
Q3. What is “Swept Volume”?
A: Swept volume is the displacement of just one cylinder. If you want to know the volume of a single cylinder, simply enter “1” in the Cylinders field above.
Sources: Spicer Parts, Performance Trends, Omni Calculator, Speedway Motors, PowerNation TV, Inch Calculator, EC Carburetors, CSG Network.