# Formula for Engine Displacement (Cubic Inches) **URL:** \ **Category:** General Discussion\ **Created:** [February 15, 2012, 11:00pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962 "2012-02-15T23:00:32Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![OmegaMan62](https://avatars.discourse-cdn.com/v4/letter/o/df705f/32.png) [@OmegaMan62](https://community.cartalk.com/u/OmegaMan62)\ **Post date:** [February 15, 2012, 11:00pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/1 "2012-02-15T23:00:32Z")
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. ---
**Author:** ![DfromSD](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/dfromsd/32/1669_2.png) [@DfromSD](https://community.cartalk.com/u/DfromSD)\ **Post date:** [February 15, 2012, 11:03pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/2 "2012-02-15T23:03:10Z")
Good info. to have. Thanks! ---
**Author:** ![doubleclutch](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/doubleclutch/32/1281_2.png) [@doubleclutch](https://community.cartalk.com/u/doubleclutch)\ **Post date:** [February 16, 2012, 3:53am UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/3 "2012-02-16T03:53:50Z")
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. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [February 16, 2012, 4:11am UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/4 "2012-02-16T04:11:50Z")
Ah, cubic inches. I remember cubic inches! I guess the world isn’t quite so metric afterall. The post is still talking about CID. ---
**Author:** ![mark9207](https://avatars.discourse-cdn.com/v4/letter/m/71c47a/32.png) [@mark9207](https://community.cartalk.com/u/mark9207)\ **Post date:** [February 16, 2012, 8:09am UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/5 "2012-02-16T08:09:24Z")
For rough estimates you can do in your head easily, 61 cubic inches is about one liter. It’s not exact, but fairly close. ---
**Author:** ![EllyEllis](https://avatars.discourse-cdn.com/v4/letter/e/f14d63/32.png) [@EllyEllis](https://community.cartalk.com/u/EllyEllis)\ **Post date:** [February 16, 2012, 9:27pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/6 "2012-02-16T21:27:37Z")
Isn’t that Radius squared instead of Bore. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [February 16, 2012, 9:29pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/7 "2012-02-16T21:29:54Z")
Nope, he divided by 4. ---
**Author:** ![EllyEllis](https://avatars.discourse-cdn.com/v4/letter/e/f14d63/32.png) [@EllyEllis](https://community.cartalk.com/u/EllyEllis)\ **Post date:** [February 16, 2012, 9:37pm UTC](https://community.cartalk.com/t/formula-for-engine-displacement-cubic-inches/70962/8 "2012-02-16T21:37:54Z")
OK I just figure R squred X P (3.14) x stroke x no of cylinders And yes, 1 liter is equal to about 61 cubic inches.