Zerdly

Grinding Circulating Load Calculator

Estimate the circulating load of a closed grinding circuit three ways — direct dry flows, a classifier percent-solids water balance, or a conserved tracer/size-fraction balance — with a sensitivity flag for unstable denominators.

100% FreeRuns in your browserIntermediate
How to use this calculator

Enter values

Calculated results

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More needed
  • Enter classifier feed, overflow and underflow % solids.

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

  1. Pick a method: direct flows, water balance (% solids), or tracer.
  2. Enter the classifier feed, overflow and underflow values for that method.
  3. Read the circulating load ratio and percent; add the fresh feed to get the circulating dry flow.

How it works

Circulating load is the recirculating (classifier underflow) stream relative to the new product. By direct flows, CL% = underflow dry ÷ overflow dry × 100. By the water balance, convert each percent solids to a liquid:solids ratio L = (1 − Cw)/Cw, then CL ratio = (L_overflow − L_feed)/(L_feed − L_underflow). By tracer, CL ratio = (x_feed − x_overflow)/(x_underflow − x_feed) for any variable conserved across the classifier split.

All three refer to the classifier (feed, overflow, underflow), never across a mill boundary — grinding changes size, so a size fraction is only conserved across classification. When the feed and underflow values are close, the denominator is small and the estimate becomes sensitive; the tool flags that rather than returning a falsely precise number.

Worked example

Classifier at 50 / 30 / 70% solids. L_feed = (1 − 0.5)/0.5 = 1.0; L_overflow = 0.7/0.3 = 2.3333; L_underflow = 0.3/0.7 = 0.42857. CL ratio = (2.3333 − 1.0)/(1.0 − 0.42857) = 1.3333/0.57143 = 2.3333, i.e. a circulating load of 233.33%.

Common mistakes

  • Using mill discharge instead of classifier feed for the balance methods.
  • Applying a size fraction across the mill (where it is not conserved) rather than across the classifier.
  • Trusting a result when feed and underflow solids are almost equal — the denominator is unstable.

Frequently asked questions

Which method should I use?

Use direct flows when you have reliable dry-flow measurements; otherwise the percent-solids water balance is the practical plant method. The tracer method suits a conserved size fraction or assay.

Is 250% circulating load high?

Closed ball-mill circuits commonly run a few hundred percent circulating load; the right value depends on the grind target and classifier efficiency. This tool measures it, it does not set a target.

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Cite this tool

Zerdly. (2026). Grinding Circulating Load Calculator. Retrieved from https://www.zerdly.com/tools/grinding-circulating-load-calculator/

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

All calculations run in your browser. Your inputs are never saved or transmitted.