Timing Belt Calculator
This timing belt calculator finds the belt length and tooth count for two toothed pulleys at a set center distance. Pick the belt profile, enter the tooth counts and center distance, and the timing belt calculator returns the nearest stock belt, the exact center distance for that belt, the speed ratio, the driven speed, and the teeth in mesh.
Results
The Timing Belt Calculator is part of our Machinery collection. Browse more machinery to size, convert, and check your work alongside this tool.
What the timing belt calculator does
Timing belts come in whole numbers of teeth, so the belt length is never free to choose. The timing belt calculator works out the pitch diameter of each pulley from its teeth and the belt pitch, computes the pitch length the drive needs, rounds it to the nearest whole tooth count, and then solves for the center distance that belt gives. You set the motor where the calculator says and the belt fits with the right tension.
Timing belt length formula
Pitch diameter comes from teeth and pitch, then the open belt formula gives the length:
The calculator then reverses the formula to find the center distance for the rounded belt, and estimates teeth in mesh on the small pulley from the wrap angle.
Timing belt calculator example
HTD 5M belt, 20 and 40 tooth pulleys, 150 mm centers, driver at 1,500 RPM:
The drive runs 2:1, so the output turns at 750 RPM, with 9.3 teeth in mesh on the small pulley. A GT2 printer drive with 20 and 60 tooth pulleys at 200 mm needs a 240 tooth belt (480 mm) at 199.59 mm centers.
How to use the timing belt calculator
Choose the belt profile; the pitch is the tooth spacing, such as 2 mm for GT2 or 5 mm for HTD 5M. Enter the teeth on the driver and driven pulleys, the center distance you want in millimeters, and the driver speed if you want the output speed. Press Calculate, then order the belt with the tooth count shown and set the shafts at the adjusted center distance.
Reading the belt teeth calculator result
Order the belt by profile, width, and tooth count, for example a 450-5M belt. The adjusted center distance is where the shafts should sit with that belt; leave some adjustment, usually a few millimeters, for installation and tensioning. Keep at least six teeth in mesh on the small pulley, since fewer teeth carry the load and can jump under shock. If the mesh is low, increase the center distance or the small pulley size.
When to use a timing pulley calculator
- Designing a 3D printer or CNC axis with GT2 belts
- Replacing a motor drive with new pulley sizes
- Picking a stock belt length for a set motor position
- Changing a drive ratio while keeping the frame
- Checking teeth in mesh on a small pulley
Common timing belt calculator mistakes
- Using outside diameter. The formula uses pitch diameter from teeth and pitch.
- Choosing a belt without adjustment. Leave room to fit and tension the belt.
- Too few teeth in mesh. Keep six or more on the small pulley.
- Mixing profiles. Match belt and pulleys exactly.
Tips for timing belt pitch and fit
- Use flanged pulleys on at least one shaft to keep the belt tracking.
- Align pulleys carefully; misalignment wears belt edges fast.
- Pick the next larger stock belt if the exact one is not available, then reset the center distance.
Timing belt center distance and tension
A synchronous drive keeps exact timing because teeth lock the belt to the pulleys, so the drive must be built around whole teeth. That is why the timing belt calculator rounds first and adjusts the center distance second. Designers usually provide an adjustment slot of about 1% of the center distance outward for tensioning and a little inward for fitting the belt over the flanges. Tension matters less than on V-belts, since the teeth carry the load, but too little lets the belt jump and too much wears bearings. For speed ratio, only tooth counts matter: a 20 to 40 tooth drive is 2:1 whatever the profile. To compare with a geared drive of the same ratio, try the gear ratio calculator.
Timing belt length formula versus V-belts
The open belt formula is the same one used for V-belts, but V-belts slip and stretch, so their length can be any value and tension is set by moving the motor. Timing belts do not slip and are sold in tooth increments, so a design that ignores the tooth count ends up a few millimeters off with no way to correct it. For a V-belt or flat belt drive, use the belt length calculator.
Timing belt pitch chart
Common synchronous belt profiles and their pitch:
| Profile | Pitch | Typical use |
|---|---|---|
| MXL | 2.032 mm (0.08 in) | Light instruments |
| GT2 | 2 mm | 3D printers and small CNC axes |
| HTD 3M | 3 mm | Small power drives |
| T5 | 5 mm | Linear motion, metric |
| HTD 5M | 5 mm | General machinery |
| XL | 5.08 mm (0.2 in) | Light imperial drives |
| HTD 8M | 8 mm | Medium power drives |
| L | 9.525 mm (0.375 in) | Medium imperial drives |
| T10 | 10 mm | Conveyors and linear axes |
| H | 12.7 mm (0.5 in) | Heavy imperial drives |
| HTD 14M | 14 mm | Heavy power drives |
Timing Belt Calculator FAQ
How do you calculate timing belt length?
Find each pitch diameter as teeth × pitch ÷ π, then L = 2C + π(D1 + D2) ÷ 2 + (D2 − D1)² ÷ 4C. Divide by the pitch and round to get the belt teeth.
How do I find the center distance for a stock belt?
The timing belt calculator solves the length formula backward for the rounded belt length and returns the center distance to set.
How many teeth should be in mesh?
Aim for at least six teeth in mesh on the small pulley. Fewer teeth raise the load per tooth and the risk of ratcheting.
Can I mix GT2 and T2.5 parts?
No. Profiles differ in tooth shape even when pitches are close, so match the belt and pulleys to one profile.