Choose the Tooth Profile

The tooth profile is the most fundamental selection decision because it determines which pulleys the belt will work with and sets the baseline for load capacity, accuracy, and noise. Once the profile is set, it cannot be changed without also replacing the pulleys.

There are two main profile families:

• Trapezoidal (straight-sided teeth): MXL, XL, L, H, XH, XXH (imperial) and T2.5, T5, T10, AT5, AT10 (metric). Best for light to medium duty, general conveyance, and cost-sensitive applications.
• Curvilinear (rounded teeth): HTD 3M, 5M, 8M, 14M (standard) and GT/GT2/GT3 (optimized). Best for high-torque drives, precision positioning, servo applications, and heavy industrial use.

If you are replacing a belt on existing equipment, match the original profile exactly. If you are designing a new drive or upgrading, curvilinear profiles (HTD or GT) are recommended for most industrial applications because they offer higher load capacity, lower noise, and reduced backlash compared to trapezoidal profiles at similar pitch sizes.

For a detailed comparison of every profile, see our Timing Belt Tooth Profiles Explained guide.

Select the Pitch

Pitch is the distance from the center of one tooth to the center of the next, measured along the belt's pitch line. It is the primary factor that determines the belt's load capacity per tooth. Larger pitch means larger teeth, which means higher torque capacity but also larger pulleys and higher minimum bend radii.

Select pitch based on the torque and speed requirements of your drive:

General rules for pitch selection:

• Higher speed, lower torque drives favor smaller pitch (more teeth in mesh, smoother operation).
• Lower speed, higher torque drives favor larger pitch (stronger teeth to handle the load).
• If your application falls between two pitch sizes, the larger pitch provides a greater safety margin. However, the larger pitch also requires larger pulleys.
• Minimum pulley size increases with pitch. Confirm that the required pulley diameters fit within your machine's physical constraints before finalizing pitch.

See our Timing Belt Pitch Chart for a complete reference of all pitches, tooth heights, and part number formats.

Determine the Belt Width

Belt width directly affects load capacity. A wider belt carries more load at the same pitch. Width selection is based on the design power of the drive, which is the required power multiplied by a service factor that accounts for the application type.

Design power = Required power x Service factor

Once you know the design power, consult the belt manufacturer's power rating tables for the chosen profile and pitch to find the minimum width that meets or exceeds the requirement. Power rating tables are published by Gates, Continental, and other manufacturers and are specific to each profile, pitch, and pulley tooth count.

Standard width availability by profile family:

Calculate the Belt Length

Timing belt length is specified as the pitch length, which is the total length measured along the belt's pitch line (the line where the tensile cord sits, at the base of the teeth). This is not the outer or inner circumference of the belt.

For a two-pulley drive with known center distance:

Belt Pitch Length = 2C + π(D1 + D2)/2 + (D2 - D1)² / (4C)

Where C = center distance, D1 = pitch diameter of the small pulley, D2 = pitch diameter of the large pulley. All dimensions in the same units (inches or millimeters).

After calculating, round to the nearest available stock belt length. Timing belts are manufactured in fixed pitch lengths (the number of teeth multiplied by the pitch). Adjust center distance to accommodate the nearest available belt length using a belt tensioner or adjustable motor mount.

For replacement belts: If the existing belt is intact, count the number of teeth and multiply by the pitch to get the pitch length. Or read the part number directly. For example, "560-8M-20" has a 560 mm pitch length. For imperial belts, "300L075" has a 30.0 inch pitch length (the first three digits divided by 10). See our How to Measure a Timing Belt guide for the full step-by-step process.

Select the Belt Material

Timing belts are available in several body materials, each suited to different operating environments. The tooth profile and pitch are the same regardless of material, so this choice is independent of the geometry decisions above.

Tensile cord options: The internal reinforcement (tensile cord) affects stretch characteristics and load capacity. Fiberglass is standard for most neoprene and HNBR belts. Steel cord provides near-zero elongation for precision linear motion. Aramid (Kevlar) offers high strength in a compact cross-section. Carbon fiber (used in Poly Chain GT) delivers the highest strength-to-weight ratio.

Verify Teeth in Mesh

The number of belt teeth engaged with the smaller pulley at any given time (teeth in mesh, or TIM) directly affects the drive's power capacity. If too few teeth are in mesh, the belt will slip or the engaged teeth will be overloaded.

• Minimum recommended: 6 teeth in mesh on the smaller pulley for most industrial applications.
• For high-torque or shock-loaded drives: 8 or more teeth in mesh is preferred.
• If teeth in mesh is below minimum: Increase the small pulley diameter, increase center distance, or add an idler pulley to increase the belt wrap angle on the smaller pulley.

The teeth-in-mesh count depends on the belt wrap angle around the smaller pulley. For a standard two-pulley drive with equal-size pulleys, the wrap angle is 180 degrees. As the speed ratio increases (pulleys become more different in size), the wrap angle on the smaller pulley decreases, reducing teeth in mesh.