SAG Mill Power Draw & Filling Calculator

Calculate SAG/AG mill motor power draw (kW and HP), total volumetric charge filling (J), grinding ball load (Jb), and critical rotational speed per Morrell C-model.

Mill Geometry & Charge

Inside Shell Diameter D (m): e.g., 28 ft to 40 ft SAG mill

Belly Length L (m):

Total Charge Filling J (%): Total ore + steel balls volume

Steel Ball Charge J_b (%): Typical SAG ball charge: 8% to 15%

Operational Speed (% of Critical Nc):

Mill Power & Speed

SAG Mill Power at Pinion:

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Motor Rating (HP):

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Critical Speed Nc (RPM):

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Operating Speed (RPM):

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Steel Ball Mass in Mill:

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Frequently Asked Questions

What is critical speed (Nc) in grinding mills?

Critical speed is the theoretical rotational velocity at which centrifugal force equals gravitational acceleration, pinning grinding media against the liner wall with zero tumbling impact.

Why do SAG mills operate at lower fill volumes (25%–30%) than ball mills (35%–40%)?

SAG mills rely on high impact energy from large falling rocks and steel balls (cataracting) onto the toe of the charge; excessive filling cushions the blow and drops grinding power efficiency.

What is the role of steel ball addition in a SAG mill?

Adding 8% to 15% volume of high-carbon steel balls (100 mm–125 mm diameter) crushes hard, intermediate-sized pebbles (critical size 25 mm–50 mm) that resist autogenous self-breakage.