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Belt Speed Calculator

Get linear belt speed from pulley diameter and RPM

How it is calculated

The belt moves one pulley circumference for every turn, so v = π × D / 1000 × N. D is the pulley diameter in millimetres (divided by 1000 to get metres) and N is the rotational speed in revolutions per minute. The result is given twice: in metres per minute, and in metres per second, which is the first figure divided by 60. Both are shown with two decimals. Diameter and RPM must be above zero, otherwise no result is produced. The figure is the ideal surface speed of the pulley; it does not subtract belt slip or stretch, and it uses the diameter you enter, so for a V-belt use the pitch diameter, not the outside diameter.

Worked example

A pulley of 150 mm turns at 1450 rpm. Circumference: π × 150 / 1000 = 0.4712 m. Speed per minute: 0.4712 × 1450 = 683.30 m/min. Divide by 60 to get seconds: 683.30 / 60 = 11.39 m/s. That is the speed of the belt surface running over this pulley.

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Common mistakes

  • Entering the diameter in centimetres or inches. The field is millimetres, so 15 for a 15 cm pulley gives a belt speed ten times too small.
  • Using the motor shaft RPM for a pulley on a gearbox or a second shaft. Use the RPM of the shaft that actually carries this pulley.
  • Entering the radius instead of the diameter, which halves the answer.
  • Using the outside diameter of a V-belt or flat-belt pulley with a thick belt. The belt runs at the pitch (effective) diameter, so the real speed is slightly different.
  • Mixing up m/min and m/s when comparing with a conveyor or machine specification.

Sources

About this calculator

Linear belt (surface) speed comes from the pulley's circumference times its rotational speed: v = π·D·N, where D is pulley diameter and N is rotational speed in revolutions per unit time — the belt travels one circumference of the pulley for every full turn, so a larger pulley or faster rotation both directly increase belt speed. On a two-pulley drive, this same relation is why a small driver pulley and large driven pulley reduce speed (and increase torque) between them.

Mechanical and industrial engineers use this calculation to size conveyor belts to a target material throughput speed, to match belt speed to a process requirement (like a sanding belt's cutting speed or a packaging line's takt time), and to select motor RPM and pulley ratios for a new belt-drive system. It's a routine check when specifying or troubleshooting conveyor systems, treadmills, and pulley-driven machinery.

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Comments (1)

  • Editorial team

    Belt speed is the same at both pulleys, so you can use it to find the driven speed: a 150 mm pulley at 1450 rpm running the belt over a 300 mm pulley turns that one at 725 rpm, half as fast. The result is the ideal surface speed with no slip, so a loaded belt will run a little slower. Check the belt maker's maximum speed rating before choosing pulley sizes. Which belt type and speed range are you working with?

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