Belt & Pulley Speed Calculator
Driven RPM, ratio, belt speed and belt length from pulley diameters and centre distance — V-belt and timing-belt notes included.
V-belts slip 1–3 % (use the smaller effective diameter under load); timing belts don't slip — use tooth counts for the exact ratio (i = z2/z1). Keep V-belt speed under ~30 m/s and the small pulley above the belt's minimum diameter. Round the computed length to the nearest stock belt and adjust C with the tensioner.
Belt & Pulley Calculator computes driven speed, ratio, belt velocity and belt length for a two-pulley drive — free, instant and private in your browser. Workshop machine builders, HVAC techs and anyone replacing or re-speeding a belt drive use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Belt & Pulley Speed Calculator
Belt & Pulley Calculator computes driven speed, ratio, belt velocity and belt length for a two-pulley drive using the standard engineering relation: n1·d1 = n2·d2; v = π·d1·n1/60000; L ≈ 2C + π(d1+d2)/2 + (d2−d1)²/4C. Worked live: 60→180 mm pulleys at 1440 RPM give 480 RPM out, an 11.3 m/s belt and ~1180 mm length at 400 mm centres. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Belt & Pulley Speed Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Belt & Pulley Speed Calculator?
- ✓Implements the real formula — n1·d1 = n2·d2 — with the substitution shown, not a black box
- ✓Built for workshop machine builders, HVAC techs and anyone replacing or re-speeding a belt drive
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate belt & pulley?+
Driven speed, ratio, belt velocity and belt length for a two-pulley drive follows n1·d1 = n2·d2; v = π·d1·n1/60000; L ≈ 2C + π(d1+d2)/2 + (d2−d1)²/4C. For example, 60→180 mm pulleys at 1440 RPM give 480 RPM out, an 11.3 m/s belt and ~1180 mm length at 400 mm centres. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Do V-belts and timing belts use the same math?+
Kinematics yes, but V-belts slip 1–3 % and use effective (pitch) diameters that shrink under load, so real driven speed runs slightly slow. Timing belts are exact — use tooth counts (i = z2/z1) and you get a zero-slip ratio like gears.
How tight should the belt be?+
V-belts: roughly 10–15 mm of deflection per metre of span under firm thumb pressure; too tight kills bearings, too loose slips and glazes. Timing belts want enough tension that the unloaded side doesn't ratchet — follow the manufacturer's frequency or force spec when available.
Is the Belt & Pulley Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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