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Belt length calculator (pulleys)

Find the belt length wrapping two pulleys, for an open (same-direction) or crossed (reversed) drive. Enter both pulley diameters and the centre distance to get the belt length, and add a driver speed to read the driven pulley RPM and the linear belt speed.

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The Belt length calculator (pulleys) turns Belt configuration, Pulley 1 diameter (driver), Pulley 2 diameter (driven), Centre distance, Length unit (all three), Driver speed (RPM, optional), Which pulley is the driver into Belt length, Length excluding correction term, Driven pulley speed (RPM), Belt (surface) speed, instantly and for free.

How to use it

  1. Enter your values: Belt configuration, Pulley 1 diameter (driver), Pulley 2 diameter (driven), Centre distance, Length unit (all three), Driver speed (RPM, optional), Which pulley is the driver.
  2. Read the result instantly: Belt length, Length excluding correction term, Driven pulley speed (RPM), Belt (surface) speed.

Frequently asked questions

What does the Belt length calculator (pulleys) actually compute?

It takes Belt configuration, Pulley 1 diameter (driver), Pulley 2 diameter (driven), Centre distance, Length unit (all three), Driver speed (RPM, optional) and Which pulley is the driver and derives Belt length, Length excluding correction term, Driven pulley speed (RPM) and Belt (surface) speed from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

7 values: Belt configuration, Pulley 1 diameter (driver), Pulley 2 diameter (driven), Centre distance, Length unit (all three), Driver speed (RPM, optional) and Which pulley is the driver. Nothing else is required — no account, no file upload.

Which “Belt configuration” option should I choose?

You can pick between « Open belt (pulleys turn same way) » and « Crossed belt (pulleys reverse) ». Each one changes what the calculator works out, so switch and compare — the default is « Open belt (pulleys turn same way) ».

When would I actually use this?

Buying the right amount at the merchant: how many tiles, how much paint, how many bags of concrete, and what it all comes to.

What is the most common mistake?

Ordering the exact calculated quantity. Cuts, breakage and pattern matching mean tiles need 10% spare and more on a diagonal layout — and a second batch rarely matches the first for colour.

What is the difference between the Belt length calculator (pulleys) and the Brick calculator?

This one returns Belt length and Length excluding correction term; the Brick calculator returns Bricks needed and Bricks per m². That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Deck stain calculator is the closest one after this: How much stain a deck needs: the surface area of the boards, the railing and the stairs, divided by the coverage of your stain — which drops for solid stains and for rough or weathered wood — times the number of coats. Enter dimensions and it returns the gallons and, optionally, the cost.

What else is worth having open alongside it?

Sod calculator and Flooring calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

The geometry is exact for the dimensions you enter. Coverage rates come from manufacturer datasheets and vary with the surface, the number of coats and how absorbent the substrate is.

Further reading

All guides →
How-toBelt Length Between Two Pulleys: The Geometry, and Why the Answer Is Not What You OrderTwice the centre distance plus both circumferences is 36 % too long. Here is the real formula, how the two straight runs and the two arcs actually add up, how far the standard approximation drifts, and what to do with a figure that is not a catalogue length.How-toHow Many Wall Studs Do I Need? Framing by Spacing and LengthCount the studs a wall needs from its length and stud spacing, then add for corners, openings and end studs so nothing is missing on framing day.How-toHow Much Paint Do You Need to Paint a Room?Estimate paint by wall area, coats and the coverage on the tin — with a worked example and the 10% rule so you buy once and match the colour.How-toHow Many Tiles Do You Need? (Floor and Wall)Estimate tiles from the area to cover and one tile's size, then add for cuts and waste. Here's the method, with an example and the 10% rule.How-toHow Much Flooring Do You Need? (With Waste)Divide the room's area by a pack's coverage, then add for cuts and waste. Here's the method, with an example and how much extra to buy.How-toHow Much Wallpaper Do You Need?Measure the wall area, divide by a roll's usable coverage, then add for pattern repeat. Here's the method, with an example and why batch numbers matter.