Belt Size Calculator
Free belt size calculator. Enter two pulley diameters and the center-to-center distance to get the V-belt or drive belt length in inches and feet, plus wrap angles.
About the Belt Size Calculator
Our free belt size calculator finds the length of a drive belt running over two pulleys. Enter the large and small pulley diameters and the center-to-center distance between their shafts, and the tool returns the belt length in inches and feet, plus the contact (wrap) angle on each pulley so you can check there is enough grip. It works for V-belts, flat belts and timing belts on fans, compressors and machinery. Everything runs in your browser — perfect for mechanics and maintenance.
Features
- Belt length from two pulley diameters and center distance
- Length in both inches and feet
- Wrap angle on the small and large pulley
- Works for V-belts, flat belts and timing belts
- Great for fan, compressor and machinery drives
- 100% client-side and private — instant results, no signup
How to use this tool
The Belt Size Calculator works right in your browser — no signup, no installation. Follow these steps:
- Measure the large pulley diameter (in).
- Measure the small pulley diameter (in).
- Enter the center-to-center shaft distance (in).
- Read off the belt length and the wrap angles.
Frequently asked questions
How do you calculate belt length for two pulleys?
The standard open-belt formula is L = 2C + 1.57 × (D + d) + (D − d)² ÷ (4C), where C is the center distance and D and d are the large and small pulley diameters. The calculator applies this and gives the length in inches and feet.
What is the wrap angle on a pulley?
The wrap angle is how many degrees of the pulley the belt touches. More wrap means more grip and less slip. A small pulley with too little wrap (under about 120°) may slip under load. The calculator returns the wrap angle on both pulleys.
Does this work for V-belts and timing belts?
Yes. The length formula is the same for V-belts, flat belts and timing belts. For V-belts, use the pitch diameter; for timing belts, confirm the tooth count matches a stock length after you get the result.
What center distance should I use?
Use the actual measured distance between the two shaft centers. If you are designing a drive, leave room for belt tension adjustment — often a slot or idler — since the calculated length is a starting point.
Is this belt calculator free?
Yes, completely free with no signup. All maths runs in your browser — nothing is uploaded or tracked.
Using the results
The Belt Size Calculator estimates quantities from your measurements and the stated assumptions. Check dimensions, product coverage and project requirements before buying materials.