ToolnozaInputs and measurement basis
Enter feed F80 and product P80 in millimeters: the sizes at which 80% of each representative sample passes. Use comparable sampling periods and sieve analysis. Do not substitute crusher setting for P80.
Feed F80 (mm); Product P80 (mm).
Formula and calculation
RR = F80/P80; size reduction (%) = 100(1 − P80/F80).
Calculate F80/P80 reduction ratio and particle-size reduction from consistent feed and product size measures.
Worked example
F80 = 150 mm; P80 = 25 mm → RR = 6:1; size reduction = 83.33%.
How to interpret the result
A 6:1 ratio describes this pair of size statistics. It does not imply every particle becomes six times smaller or that the machine will maintain the same ratio under every feed condition.
Changing ore hardness, moisture or feed distribution can alter product size. Compare ratios with throughput and product specification rather than using the highest ratio as a goal.
Assumptions and limits
A size-ratio calculation, not equipment selection or power prediction. F80 must be at least P80 for a reduction process. Maximum-lump ratios use a different basis and should not be compared directly.
Frequently asked questions
Is P80 the closed-side setting? No. P80 is a measured product-size statistic. Closed-side setting is a machine adjustment and may influence the distribution without equaling P80.