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Pulley Calculator
Estimate the pitch length and speed relationship for a simple open belt between two pulleys. Enter dimensions in the same unit.
How do you calculate belt length between two pulleys?
For an open two-pulley drive, this calculator uses a common approximation based on center distance and the two pulley diameters. It also estimates driven RPM from the diameter ratio, assuming no slip.
Frequently asked questions
How do you calculate belt length between two pulleys?
For an open two-pulley drive, this calculator uses a common approximation based on center distance and the two pulley diameters. It also estimates driven RPM from the diameter ratio, assuming no slip.
Are my measurements uploaded?
No. All calculations and the sketch are generated in this browser; your measurements are not uploaded or saved.
What is the approximate belt-length formula?
A common open-belt pitch-length approximation is L ≈ 2C + 1.57(D + d) + (D − d)²/(4C), where C is center distance and D and d are the larger and smaller pulley pitch diameters. Actual belt selection should use the manufacturer’s pitch and sizing data.
How does pulley diameter change RPM?
With no slip, driven RPM is approximately input RPM multiplied by driver diameter and divided by driven diameter. A larger driven pulley reduces speed; a larger driver pulley increases it.
Does this calculator include belt slip or tension?
No. It is an ideal geometry and ratio estimate for an open two-pulley layout. It does not account for slip, tension, belt construction, load, wear or catalog belt sizes.
Can I use the estimate to order a belt?
Use it as a first estimate only. Confirm belt pitch, profile, effective length, center adjustment and manufacturer sizing tables before buying or operating a drive.