Pulley & Belt Calculator

Size the pulleys between your motor and your triplex pump. Drag, slide, or type. The drawing updates as you go.

Drag the pump pulley left or right to change the center distance.

Motor Pulley Diameter (in)

Pump Pulley Diameter (in)

Motor RPM

Center Distance (in)

Triplex Pump (optional)

From the pump's data plate. Leave blank to skip.

Pump Rated RPM

Pump Rated GPM

The Math

Pump RPM = Motor RPM × Motor pulley ÷ Pump pulley

Belt length = 2C + π(D + d) ÷ 2 + (D − d)² ÷ 4C

Wrap on small pulley = 180° − 2 · asin((D − d) ÷ 2C)

Belt speed (ft/min) = π × d × RPM ÷ 12

D and d are the large and small pulley diameters, C the center distance, all in inches. Use pitch diameters for exact belt length; outside diameter is close enough to pick a belt. Classical A and 4L sizes are estimated from the pitch length: A size ≈ length − 1.3", 4L size ≈ length + 0.7".

Why It Matters for a Triplex

A triplex pump's flow is fixed by its speed. Run it slower than rated and you get proportionally less water; run it faster and you wear out packings and valves. Most snowmaking-size triplex pumps are rated around 1,450 to 1,750 RPM, so a 1,725 RPM motor usually drives them through a reduction. Enter the pump's rated RPM and GPM above and this page sizes the pulley and tells you the flow you will actually get.

Then size your nozzles for that flow on the Nozzle Number Calculator, and your motor on the Pump Horsepower Calculator.