Crusher Reduction Ratio Calculator

The reduction ratio is simply how many times a crusher shrinks the rock: reduction ratio = feed size ÷ product size.

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Enter Values

Feed size — F80 or max feed

Product size — P80 or CSS

Number of crushing stages (for per-stage ratio)

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the feed size (F80, or the maximum feed size) in millimetres.
Enter the product size (P80, or the closed-side setting / CSS) in the same size measure and unit.
Optionally enter the number of crushing stages to see the average per-stage ratio, then read the reduction ratio and the single- vs multi-stage guidance.

How it works

The reduction ratio is simply how many times a crusher shrinks the rock: reduction ratio = feed size ÷ product size. Both sizes must be the same kind of measurement — either the 80% passing sizes (F80 and P80) or the maximum feed size and the closed-side setting (CSS) — because the ratio is dimensionless and only compares like with like.

Because feed and product are in the same units, the units cancel and the result is a pure number written as R : 1 (for example 5 : 1). Individual crushers have practical limits — jaw and gyratory units typically achieve about 3:1 to 7:1 and cones a little less — so a large overall reduction is split across multiple stages. If you enter a stage count, the tool takes the nth root of the overall ratio to show the average ratio each stage must deliver.

Worked example

Jaw crusher: 400 mm feed to 80 mm product. A primary jaw crusher takes run-of-mine rock with an 80% passing feed size (F80) of 400 mm and produces a product with a P80 of 80 mm. Reduction ratio = 400 ÷ 80 = 5.00 : 1 — comfortably within the ~3:1 to 7:1 a single crushing stage can deliver.

Common mistakes

Mixing size measures — comparing an F80 feed to a CSS product, or mixing mm with inches. Use the same definition and the same unit on top and bottom.
Entering a product size larger than the feed size. A crusher reduces material, so the product must be smaller than the feed; otherwise the ratio is meaningless.
Expecting one crusher to hit a very high ratio (say 20:1) in a single pass. Real crushers are limited per stage, so high overall reductions need two or more stages.

Frequently asked questions

Should I use F80/P80 or max feed / CSS?

Either works as long as you are consistent. F80/P80 (the 80% passing sizes) give a ratio that reflects the bulk of the material and is the standard in comminution work. Maximum feed size divided by the closed-side setting (CSS) is a quick machine-selection check. Just don't mix them — put the same measure on top and bottom.

What is a normal reduction ratio for a crusher?

As a rough guide, single-stage jaw and gyratory crushers deliver about 3:1 to 7:1, and cone crushers a little less. Ratios much above that generally mean the duty is spread over two or more crushing stages. This tool is guidance only — confirm against the manufacturer's data and your plant's testwork.

Is the reduction ratio dimensionless?

Yes. Because feed and product are measured in the same units, the units cancel and the result is a pure number, conventionally written as R : 1 (for example 5 : 1).

Tip: Enter any known values to calculate the remaining results.

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