# Formula for Engine Displacement (Cubic Inches)

From all the intelligent, interesting posts on this forum, I’d gather that many, if not most contributors know the mathematical formula for the cubic inch dispacement of a piston engine. For those who don’t, and wondered what it was, here it is: Bore squared (bore X bore), times Stroke, times Pi (3.14), times # of cylinders, divided by 4. For example, for a Chevy 350 v8, with a 4" bore and a 3.48" stroke, using this formula shows a displacement of 349.67 cubic inches, or 350 when you round it off; if you use a Chevy 250 i6 as your example, the bore is 3.87" and the stroke is 3.53", giving a displacement of 249.01 cubic inches (250 when rounded up). If we do this with a Ford 289 v8 (4" stroke X 2.87" bore), the resulting dispacement is 288.38 cubic inches (or 289 when rounded up). This formula will work with any size engine, any # of cylinders. Just thought I’d post this for general information.

Good info. to have. Thanks!

Another way that works is (bore/2)² X π X stroke X number of cylinders.

Another fun bit of info: The conversion factor for cubic inches to liters is .01639 eg. 350 X .01639=5.7635. Divide to convert liters to CI.

Ah, cubic inches. I remember cubic inches!

I guess the world isn’t quite so metric afterall. The post is still talking about CID.

For rough estimates you can do in your head easily, 61 cubic inches is about one liter. It’s not exact, but fairly close.