Engine Cubic Inch Calculator

Engine displacement is the total volume all the pistons sweep as they travel from top dead center to bottom dead center, quoted in cubic inches on American engines: the 350, the 383 stroker, the 454 big block. Enter the bore, the stroke and the number of cylinders, and this calculator returns the total displacement, the displacement per cylinder, and the same size in liters. It does one calculation and shows its work. It does not estimate horsepower or torque, which depend on far more than swept volume.

The three inputs must be in inches. If your specifications are in millimeters, convert them first (millimeters divided by 25.4). The cylinder count is picked from a list covering common layouts from 3 to 16 cylinders.

Quick Answer

How to use the engine cubic inch calculator

Enter three values, then click Calculate. The results stay hidden until you do.

1. Bore, in inches: the finished diameter of one cylinder. If the block has been bored oversize, enter the finished size, not the factory size: on a rebuilt 350 that usually means 4.030 in, not 4.000 in.
2. Stroke, in inches: how far the piston travels, set by the crankshaft throw. A stroker build changes this figure: the 383 combination keeps a 4.030 in bore and stretches the stroke to 3.75 in.
3. Number of cylinders: pick the count from the list, then read the total first, followed by the per-cylinder figure and the liters conversion.

If your specification sheet is metric, divide millimeters by 25.4 first. An 86.0 mm by 86.0 mm four-cylinder becomes 3.386 in by 3.386 in, which calculates to 122.0 CID, the 2.0 liter class. For general cylinder volume rather than an engine, the cylinder capacity calculator works in the geometry directly.

The cubic inch displacement formula

One cylinder is a round tube whose cross-section is a circle with the bore as diameter, so the area is (π ÷ 4) × bore². Multiply by the stroke for the volume one piston sweeps, then by the number of cylinders for the engine.

The π/4 factor is where hand calculations go wrong. It comes from the circle area formula, πr², with the radius written as half the bore: squaring the bore and multiplying by π alone overstates the area fourfold. Speedway Motors publishes the same relationship in its bore and stroke formula guide, worked with π rounded to 3.14, which is why its sample answer for the 350 combination is 349.67 rather than the 349.8 returned here with full-precision π.

Worked example: the 350 small block, step by step

Take the best-known combination in American engines: 4.00 in bore, 3.48 in stroke, 8 cylinders.

Every row is a real run of this calculator, so you can type any of them in and get the same figures back.

How the classic combinations compare

Scaled to the 454 big block:

Bore versus stroke: oversquare, square and undersquare

The badge under your result names the engine's character, and it is read straight off the two numbers you entered.

• Oversquare (bore larger than stroke): the 4.00 by 3.48 small block is oversquare. A wide, short cylinder leaves room for larger valves and shortens piston travel per revolution, suiting higher engine speeds.
• Undersquare (stroke longer than bore): many truck and economy engines are undersquare. The crank's longer lever arm tends to favor low-speed torque, at the cost of higher piston speed at any given rpm.
• Square (bore equal to stroke): the 3.386 in by 3.386 in four-cylinder in the table is square, a common modern compromise whose 122.0 CID is the classic 2.0 liter class.

Character is a tendency, not a verdict: gearing, cam timing, forced induction and tuning move real engines a long way from what bore and stroke alone suggest.

Overbores and stroker cranks: where extra cubes come from

There are exactly two ways to grow an engine, and they do not grow it equally.

Stroke grows displacement in proportion. Stretching a 350's stroke from 3.48 in to 3.75 in multiplies displacement by 3.75 ÷ 3.48, about 7.8 percent, which on the bored block in the table takes 355.1 CID to 382.7 CID: the 383 stroker recipe, a common overbore plus a longer crank.

Bore grows displacement faster than in proportion, because it is squared. The 0.030 in overbore that sounds like cleanup machining takes the 350 from 349.8 to 355.1 CID, a gain of 5.3 CID from three-hundredths of an inch. It also thins the cylinder walls, so how far a block can be bored is a machine shop question, not a calculator question.

Racing classes that cap displacement are why this arithmetic belongs before parts are ordered: 355.1 CID does not enter a 350-cubic-inch class, whatever the fender badge says.

Cubic inches, cubic centimeters and liters

All three units describe the same swept volume. This calculator takes inches in and returns cubic inches and liters out. It does not print a cubic centimeter figure, so convert when you need one: 1 cubic inch is 16.3871 cc, so the 349.8 CID small block is about 5,733 cc, and its 5.73 liters is that figure divided by 1,000.

Older versions of this page listed cubic centimeters and a bore-to-stroke ratio among the outputs; the tool has never printed either. If you work mainly in metric sizes, the cc calculator handles cubic centimeter figures directly, and the cc to inches calculator converts a metric displacement into cubic inches.

What displacement does not tell you

Displacement is the starting point of an engine build, not the answer to it.

• Not compression ratio: compression also needs chamber volume, piston dish or dome, deck height and gasket thickness, none of which are inputs here. A stroke change alters compression on its own, which is why stroker kits ship with matched pistons.
• Not power: two 350s can differ by hundreds of horsepower. Head flow, camshaft, induction, exhaust and tuning decide where a displacement lands.
• Not the whole size story: manufacturers round, sometimes with marketing in mind: a modern "5.0" can measure closer to 4.95 liters. Trust the dimensions over the badge.
• Not a fitment check: a longer stroke needs crank, rod and piston combinations that physically clear the block and each other. Arithmetic that fits here does not mean parts fit in the engine.

Common mistakes in displacement calculations

• Using the factory bore on a rebuilt engine. Most classic blocks today are bored 0.030 in or more over, which understates a 350 by 5.3 CID.
• Feeding the formula the radius, or mixing units. The formula wants bore squared times π/4: the radius instead of the bore quarters the answer, and an 86 mm bore entered as 86 destroys it. Convert millimeters to inches first.
• Rounding mid-calculation. Rounding the per-cylinder figure before multiplying by the cylinder count can move the total by several cubic inches. This calculator rounds only at the end.
• Counting cylinders wrong. The per-cylinder result is a useful check: if it looks like a whole small engine, the count is set wrong.

What competing calculators miss

• Rounded-π tools drift: Speedway Motors works its published example with π as 3.14 and lands on 349.67 for the 350 combination. This calculator uses full-precision π and returns 349.8.
• Reverse modes invite unit errors: Omni Calculator's tool also solves backwards for bore and accepts millimeters, but a backwards solve on a mistyped unit returns a confident, wrong bore size. This tool runs one direction, in inches, with inputs echoed in the results so a slip is visible.
• Metric-first tools bury the cubic inch answer: ProCarManuals and similar pages lead with cc and liters from millimeter inputs, which serves modern engines well and classic American ones badly: small-block Chevrolet factory specifications were published in inches.
• Few show the per-cylinder figure: Sage Calculator and CalculatorDock present the total and a liters conversion, but the per-cylinder displacement shown here is the quickest sanity check on a build sheet, and the number piston and ring packages are chosen against.

Frequently asked questions

Add This Calculator to Your Website

References