Quoting a Metric Displacement on a US Spec Sheet
Fluid-power hardware is designed in millimetres and rated in cubic centimetres per revolution or litres per stroke. The catalogues, sizing tables and datasheets that specify it in North America are still written in cubic inches. Anyone matching a European gear pump to an American motor, sizing a cylinder against an existing circuit, or filling in a US supplier's selection sheet ends up making the same translation again and again.
What the Number Actually Describes
Volume moved per revolution
Volume swept per stroke
Catalogues that never went metric
Geometry first, delivery second
Turning a Nameplate Rating Into Catalogue Units
Most of the time you have a cc or litre figure from a nameplate, a European datasheet or your own bore-and-stroke calculation, and you need it in the units the US sizing sheet expects.
Enter the metric displacement
Type the litre figure directly, or pick cc on the left and enter the nameplate rating as it is printed — 8, 16, 22, 32, 45. Cubic inches appear on the right as you type, and spaces or a comma decimal separator are handled for you.
Keep the "per what" in your head
The converter handles volume; the per-revolution or per-stroke part rides along unchanged. Convert 0.032 L to 1.9528 in³ and it is still per revolution — write the unit back in before the number goes on a drawing.
Copy it into the sizing calculation
The copy button puts the bare number on the clipboard with no unit and no spaces, ready for a spreadsheet cell that then multiplies by shaft speed. Ctrl + C inside a field does the same.
Reverse it for an American part
When the datasheet in front of you is already in cubic inches and the drawing needs metric, press the swap button (↔) for in³ → L. By hand, divide by 61.0237441, or multiply by 16.387064 to land in cc.
Pump, Compressor and Cylinder Swept Volumes
Typical metric ratings from fluid-power and compressed-air hardware, with the cubic-inch equivalent a US catalogue or sizing formula would use.
| Component | Metric rating | Litres | Cubic inches |
|---|---|---|---|
| Small gear pump | 8 cc/rev | 0.008 L | 0.4882 in³/rev |
| Mid-range gear pump | 16 cc/rev | 0.016 L | 0.9764 in³/rev |
| Larger gear pump | 32 cc/rev | 0.032 L | 1.9528 in³/rev |
| Axial-piston pump | 45 cc/rev | 0.045 L | 2.7461 in³/rev |
| Cylinder, 50 mm bore × 200 mm stroke | 392.7 cc/stroke | 0.3927 L | 23.96 in³/stroke |
| Cylinder, 80 mm bore × 400 mm stroke | 2010.6 cc/stroke | 2.0106 L | 122.69 in³/stroke |
| Cylinder, 100 mm bore × 600 mm stroke | 4712.4 cc/stroke | 4.7124 L | 287.57 in³/stroke |
| Twin-cylinder compressor pump | 463.3 cc/rev | 0.4633 L | 28.27 in³/rev |
The cylinder figures are cap-side volumes, calculated as π/4 × bore² × stroke. Subtract the rod area for the retract side. The compressor row is the swept volume of both bores together — multiply it by shaft speed and divide by 1728 to reach a displacement figure in cubic feet per minute.
Handy Behaviour When Sizing Hardware
Nameplate figure in, catalogue figure out
Both fields update live, so you can walk a whole pump range — 8, 11, 16, 22, 32, 45 cc/rev — and read the cubic-inch column straight off.
Flip when the datasheet is American
The swap button turns the page into in³ → L for the times a US component has to be described on a metric drawing.
cc, mL, litres or m³ on either side
Searchable dropdowns hold every volume unit, so a rating printed in cc needs no scaling by hand before it is converted.
Small displacements keep their decimals
Results carry up to eight decimal places and shift to scientific notation for very small volumes, so a fraction of a cubic inch does not collapse to zero.
Fluid Power and Compressed Air Questions
What does "displacement" mean on an air compressor pump?
It is the swept volume of the pump's cylinders in one revolution — piston area times stroke, added up across the bores. Nothing about air quality, pressure or losses is included. A twin-cylinder pump sweeping 0.4633 L (28.27 in³) per revolution is describing its geometry only.
Is the CFM on a compressor label the same as its pump displacement?
No, and mixing them up is how undersized machines get bought. Displacement CFM comes straight from the geometry: swept volume in cubic inches × rpm ÷ 1728. The 28.27 in³ pump at 800 rpm gives about 13.1 CFM on paper. Free air delivery — what actually comes out of the port at a stated pressure — is meaningfully lower, so always compare tools against the delivered figure.
Why do US hydraulic catalogues quote in³ per revolution or per stroke?
Because the rest of the American sizing chain is imperial. A US gallon is exactly 231 in³, so flow in gpm is displacement in in³/rev × rpm ÷ 231 — a one-step calculation if the displacement is already in cubic inches. Keep it in cc and you carry a conversion through every formula.
How do I work out swept volume from a bore and stroke given in inches?
Piston area is π/4 × bore², and volume is that area times the stroke. A 4 in bore gives 12.566 in² of area, so a 24 in stroke sweeps 301.6 in³ — about 4.94 L per full extension. For the retract side, subtract the rod's cross-sectional area from the piston area before multiplying.
My pump nameplate says 22 cc/rev — what is that in cubic inches?
22 cc is 0.022 L, which is 1.3425 in³ per revolution. Driven at 1800 rpm that is a theoretical 39.6 L/min, or 1.3425 × 1800 ÷ 231 ≈ 10.5 gpm before volumetric efficiency is taken off. Real delivery at working pressure will be a few per cent under that.
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