Belt Length Calculator
Approximate belt length and wrap angle on the small pulley from two diameters and centre distance.
Results
Length
1759.2
mm
Angle
165.64
°
Gear ratio
2.5000
Rotational speed
580.0
rpm
Speed
7.592
m/s
What this tool does
This is the standard approximation used to pick a belt before ordering, accurate to well under a percent for normal drive geometries. The wrap angle on the smaller pulley is shown too, because a wrap much below 120° starts to limit the power the belt can transmit.
Formula
L ≈ 2C + π(D + d)/2 + (D − d)² ÷ (4C)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
dd | Diameter | mm |
d | Diameter | mm |
c | Distance | mm |
rp | Rotational speed | rpm |
L | Length | mm |
ang | Angle | ° |
RT | Gear ratio | — |
N2 | Rotational speed | rpm |
VB | Speed | m/s |
Worked example
- Diameter250 mm
- Diameter100 mm
- Distance600 mm
- Rotational speed1450 rpm
- Length1759.2 mm
- Angle165.64 °
- Gear ratio2.5000
- Rotational speed580.0 rpm
- Speed7.592 m/s
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.