Mill Power Requirement Calculator

Work out mill power requirement instantly with clear inputs, formula shown and shareable results.

About Mill Power Requirement Calculator

Bond's law gives specific grinding energy as 10 x work index x (1/sqrt(P80) - 1/sqrt(F80)) in kilowatt-hours per tonne, with sizes in microns. Multiplying by throughput gives mill power. Comminution typically consumes 30-50% of a concentrator's total energy, so the work index and target grind size dominate operating cost.

Formulas

Bond's law

W (kWh/t) = 10 x Wi x (1/sqrt(P80) - 1/sqrt(F80))

Mill power

Power (kW) = specific energy x throughput (t/h)

Worked example

With the default values below, Mill Power Requirement Calculator returns Mill Power Required of 5.0765. Change any input above and every figure here is recalculated in your browser.

Inputs used

Mill Throughputminimum 0 t/hour: 500 t/hour
Bond Work Indexminimum 0.01 kWh/t: 14 kWh/t
Feed 80% Passing Sizeminimum 0.01 micron: 12,000 micron
Product 80% Passing Sizeminimum 0.01 micron: 150 micron

Results

Mill Power Required: 5.0765
Specific Grinding Energy: 10.1529
Size Reduction Ratio: 80.00
Annual Energy At 90% Utilisation: 40,022.9

Step by step

1Values used
2Bond's law
3Mill power
4Mill Power Required= 5.0765
5Specific Grinding Energy= 10.1529
6Size Reduction Ratio= 80.00
7Annual Energy At 90% Utilisation= 40,022.9

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does grinding finer cost so much more?

Energy scales with the inverse square root of product size, so halving P80 raises specific energy by about 41%. Grinding only as fine as liberation requires is a major cost lever.

Is Bond's law always applicable?

It works well for conventional ball milling in the 100 micron to 10 mm range. Very fine grinding follows a different exponent, and SAG milling needs its own testwork and models.