How to Choose a Timing Belt

Start with the Pulley, Not the Belt

A timing belt must match the pulley it runs on — the pitch is non-negotiable. Measure or read the pulley’s tooth pitch first: 2 mm means GT2, 3 mm means 3GT, 5 mm means HTD 5M or T5, 8 mm means HTD 8M, 14 mm means HTD 14M. Trapezoidal profiles (T/AT, MXL/XL/L/H) are straight-sided; curvilinear (HTD/GT) are rounded. Match both pitch and profile.

The Five Decisions, in Order

1. Pitch (Match the Pulley)

For a new drive, pitch is chosen by torque and speed:

Pitch	Torque	Typical Use
GT2 (2 mm)	Light	3D printers, small stages
HTD 5M	Medium	Actuators, small conveyors
HTD 8M	Medium-high	Packaging, general power transmission
HTD 14M	High	Heavy industrial drives

Heavier load or higher speed pushes you up the pitch ladder. If you are replacing a belt, match the existing pitch exactly — nothing else fits.

2. Width (Carry the Load)

Width is the load knob. At the same pitch, torque capacity scales roughly with width: a 15 mm belt carries about 1.7x the torque of a 9 mm belt. Practical widths:

• GT2: 6 mm (printers), 9-10 mm (heavier gantries)
• HTD 5M: 6-30 mm
• HTD 8M: 9-50 mm
• HTD 14M: 20-85 mm

When in doubt, size up. Belt width is cheap relative to a failed drive.

3. Length (Fit the Drive)

For endless belts, length must equal a whole number of teeth × pitch (e.g. an HTD 8M belt is 8 mm × teeth count). Measure the center distance and pulley sizes, then calculate:

Belt length = 2 × center distance + π × (D1 + D2) / 2 + (D2 - D1)² / (4 × center distance)

…where D1 and D2 are the pulley pitch diameters. Round up to the nearest whole tooth count. For open-ended belts, measure the required run and order with margin for the tensioner.

4. Tension Member (Match the Duty)

Tension Member	Stiffness	Best For
Fiberglass	Low stretch	Standard drives, economy
Aramid (Kevlar-type)	Medium	Shock loads, high speed
Steel	Highest	Precision linear drives, heavy loads

The tension member carries the working load. Shock and start-stop duty want aramid; precision positioning wants steel; steady loads are fine with fiberglass.

5. Material (Match the Environment)

Environment	Material
Standard industrial	Polyurethane or rubber
Wash-down / food	Polyurethane (food-grade available)
High temperature	Rubber (chloroprene)
Static-sensitive	Anti-static polyurethane
Chemical / abrasive	Polyurethane

Measuring an Existing Belt

To replace a belt you already have: (1) measure the tooth pitch with a caliper, (2) measure the width, (3) count the teeth (endless) or measure the length (open-ended), (4) note the profile shape (rounded vs trapezoidal). That is everything needed for a replacement order — send us a photo if the belt is marked.

Common Mistakes to Avoid

• Matching pitch but not profile — an HTD pulley needs HTD teeth; a trapezoidal T-pitch pulley needs T teeth. The numbers can look similar (5M vs T5) but they are not interchangeable.
• Under-sizing width — the belt stretches, skips, or fails early. Use the load to size width, not the old belt’s width.
• Ordering an endless belt one tooth too short — it will not fit. Measure twice, round up.
• Ignoring the environment — a rubber belt in a wash-down line fails fast; a polyurethane belt in a hot engine bay fails fast. Match material to environment.
• Forgetting the tensioner range — the belt must fit the drive at the tensioner’s mid-travel, not at the end stops.

Quick Sizing Flow

1. Pulley pitch and profile → lock the belt pitch
2. Load and speed → width
3. Center distance and pulleys → length (whole teeth)
4. Duty (shock/steady/precision) → tension member
5. Environment → material
6. Confirm tensioner travel fits → order

If you send us the motor power, speeds, center distance, and environment, we will size the complete drive — belt, pulleys, and tensioner recommendation.

Related Guides

• Timing Belt vs V-Belt
• Custom & OEM Services [Timing Belt Length Calculator] [Timing Belts 101] [Timing Belt FAQ] [Request a Quote]