Timing Belt Pulley Calculator

Precise pitch diameter, belt length, center distance & teeth in mesh. Supports metric pitches & custom. Fixed linear chart, smarter custom pitch. Trusted by engineers.

Pitch diameter: Dp (mm) = (N · p) / π

Belt length (approx): L = 2C + (π/2)(D₁+D₂) + (D₂-D₁)²/(4C)

Teeth in mesh (small pulley): Tim = (0.5 – (D₂-D₁)/(6C)) · N₁

All dimensions in mm. Valid for open drives.

mm
Reference only
mm
GT2: 20T/60T, C=100
HTD5: 18T/36T, C=120
HTD8: 22T/44T, C=150
XL: 15T/30T, C=200

Understanding Timing Belt Drives

Timing belts (synchronous belts) provide positive, slip‑free power transmission. The pulley tooth profile meshes with belt teeth — accurate center distance and belt length are critical for backlash-free motion.

Pitch diameter formula:

Dp = (N · p) / π

Where N = number of teeth, p = belt pitch (mm).

Key Parameters & Effects

Parameter Effect on Drive Typical Range
Belt pitch (p) Larger pitch = higher power, larger minimum teeth 2 mm (3D printer) – 12.7 mm (XL)
Small pulley teeth Below ~12 may cause ratcheting 16 – 30 (GT2/HTD)
Center distance Too short → insufficient mesh; too long → tension issues ≈ 0.5(D₁+D₂) to 3(D₁+D₂)
Teeth in mesh (TIM) Aim for ≥6 to prevent tooth skipping 6 – 12

Practical Design Workflow

1
Select belt pitch based on load and speed.
2
Choose pulley teeth – ensure N₁ ≥ minimum recommended for pitch.
3
Set center distance roughly, then compute belt length. Adjust to nearest standard length (if needed).
4
Verify teeth in mesh and adjust if <6.

Applications

  • 3D printers & CNC routers: GT2/GT3 belts for positioning
  • Automotive engines: timing belts (HTD profiles)
  • Conveyors: heavy duty T10 / AT20
  • Robotics: lightweight synchronous drives

⚡ Calculator highlights:

  • Instant pitch diameters & speed ratio
  • Belt length estimation + belt teeth count (approx)
  • Teeth in mesh with visual warning
  • Interactive L vs C chart (linear scale, accurate red dot)
  • Custom pitch with smart fallback

Frequently Asked Questions

The formula used is for open belt drives and assumes ideal geometry. True belt length is a multiple of pitch, but this gives a close estimate. Use it to select the nearest standard belt length.

Most manufacturers recommend at least 6 teeth in mesh on the small pulley. Below that, the belt may skip teeth under load. Increase center distance or use an idler to improve mesh.

Belt width does not influence pitch diameter or length calculation. It affects power capacity and tension. We include it as reference only.