GT2 belt drive calculator
Set your pulley sizes and belt length to find the ratio, output speed and the distance you need between shaft centres. Matching parts are listed underneath.
Drive
Belt width
Filters belts and pulleys
Belt
Length range
Loading drive geometry…
Ratio
—
Output speed
—rev/min
Centre distance
—mm
Parts for this drive
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Total
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How these numbers are worked out
| Pitch diameter | PD = N × p ÷ π, with p = 2 mm for GT2. A 20 tooth pulley is 12.73 mm PD. |
|---|---|
| Ratio | Driven teeth ÷ driver teeth. Above 1 the drive reduces speed and multiplies torque. |
| Output speed | Motor speed ÷ ratio. Both pulleys turn the same way on an open belt. |
| Centre distance | Solved from the exact belt-wrap geometry rather than the usual approximation: L = 2C·cos α + (π + 2α)·R + (π − 2α)·r, where α = asin((R − r) ÷ C). The calculator solves that for C numerically. |
| Teeth in mesh | Counted on the smaller pulley from its wrap angle. Fewer than 6 and the belt is liable to skip under load. |
| Adjustment | Centre distance is nominal at zero tension. Allow movement at one shaft, or use an idler, to take up tension and tolerance. |
