Free Belt Drive Calculator
Calculate speed ratio and belt length for a two-pulley belt drive system.
mm
mm
mm
RPM
Driven Pulley Speed
875.0 RPM
Speed Ratio2.000
Approx. Belt Length1,718 mm
Driven Pulley Speed vs Driver Pulley Diameter (D1)
Belt Drive Speed and Belt Length
Belt drives transmit power between shafts using friction between a belt and pulleys.
Speed Ratio
N2 = N1 x D1 / D2 (assuming no belt slip)
Belt Length (open drive)
L = 2C + pi(D1 + D2)/2 + (D2 - D1)^2 / (4C)
where C is the shaft centre distance. This approximate formula works well for standard configurations.
Example Calculation
150 mm driver at 1750 RPM driving a 300 mm pulley, centres 500 mm apart.
- 01Speed ratio = 300/150 = 2.0
- 02Driven speed = 1750 / 2.0 = 875 RPM
- 03Belt length = 2x500 + pi(150+300)/2 + (300-150)^2/(4x500)
- 04L = 1000 + 706.9 + 11.25 = 1718 mm
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