Engine Bore & Stroke Calculator
Use this engine displacement calculator to compute total displacement, or solve for unknown bore or stroke based on your target engine size.
Tip: In metric mode, enter displacement target in cc. In imperial mode, enter target in cubic inches.
What this engine bore stroke calculator does
This bore and stroke calculator helps engine builders, tuners, and enthusiasts quickly compute engine displacement and bore-to-stroke geometry. You can use it in three ways:
- Calculate displacement from known bore, stroke, and cylinder count.
- Calculate stroke from bore, cylinders, and target displacement.
- Calculate bore from stroke, cylinders, and target displacement.
It supports both metric and imperial workflows, making it useful for motorcycle, automotive, marine, and racing applications.
Understanding bore, stroke, and displacement
Bore
Bore is the diameter of each cylinder. A larger bore increases piston area, which can increase airflow potential and high-rpm power when matched with the right head and cam setup.
Stroke
Stroke is how far the piston travels from top dead center (TDC) to bottom dead center (BDC). A longer stroke generally increases leverage on the crankshaft, often favoring torque output.
Displacement
Engine displacement is the total volume swept by all pistons during one full stroke. It is commonly shown in:
- cc (cubic centimeters)
- L (liters)
- cu in (cubic inches)
How to use the calculator
Mode 1: Calculate displacement
Enter bore, stroke, and cylinder count. Click calculate to get total engine size in cc, liters, and cubic inches.
Mode 2: Calculate stroke
Enter bore, cylinder count, and your target displacement. The tool solves for the required stroke.
Mode 3: Calculate bore
Enter stroke, cylinder count, and target displacement. The tool solves for the required bore diameter.
Why bore/stroke ratio matters
The calculator also reports bore/stroke ratio, which is a quick way to describe engine geometry:
- Oversquare (ratio > 1.05): Bore is larger than stroke. Often supports higher rpm.
- Square-ish (0.95 to 1.05): Balanced geometry for broad performance.
- Undersquare (ratio < 0.95): Stroke is longer than bore. Often emphasizes low-end and midrange torque.
Ratio alone does not determine power; cam timing, head flow, compression, intake/exhaust design, and fueling all matter. But ratio is still a very useful first-pass design metric.
Example calculations
Example 1 (metric): 86 mm × 86 mm, 4 cylinders
This setup is essentially a square engine and comes out near 1998 cc (2.0L), a classic modern four-cylinder size.
Example 2 (imperial): 4.030 in × 3.480 in, 8 cylinders
This computes to roughly 355 cubic inches, a common small-block V8 configuration.
Common mistakes to avoid
- Mixing units (for example, mm bore with cubic-inch target).
- Entering radius instead of diameter for bore.
- Forgetting to multiply by total cylinders in manual calculations.
- Ignoring practical limits like block wall thickness and crank clearance.
Quick FAQ
Is this an engine displacement calculator?
Yes. It calculates total displacement and can also solve inverse bore/stroke problems.
Can I use it for motorcycles and single-cylinder engines?
Absolutely. Set cylinders to 1 (or any count) and use your measured bore and stroke.
Does this replace full engine simulation?
No. This is a geometry and displacement tool. Detailed performance still requires airflow, compression, ignition, and dyno-based analysis.