CalipERD™ Rim Measuring Device



A caliper to measure ERD – Effective Rim Diameter – used in spoked wheel building.

Product Description

This tool measures Effective Rim Diameter – the most critical dimension when determining spoke length.

Current methods to measure rims are clumsy and imprecise. That’s why this tool exists.

Accurate, Precise, Repeatable, Fast. This will allow a perfect spoke length by determining the correct nipple seat diameter. The adjustable window can be used to add nipple height (x2), allowing a one-shot exact ERD measurement.

  • Provides direct measurement of a rim
  • Adjustable calibration window
  • Measures nearly any rim!
    • up to 750mm reliably (fits 32″ and 36″ rims)
    • 125mm minimum (~ 12″)
    • 53mm throat/swing/reach distance – fits most fatbike rims
  • Precise to within .5mm
  • Interchangeable Feelers for different applications
    • includes Standard Nipple Set only (Effective February 2024)
  • Includes calibration tube


Use cases include:

  • Verifying Manufacturer Stated dimensions
    • (are they suggesting an actual ERD? Based on which nipple?? Do they mean Nipple Seat Diameter?)
  • Checking factory specifications
  • Obtaining Data-driven roundness of a rim





Additional Information

Weight 475 g
Dimensions 39 × 5 × 7 in
Knob Color

Orange, Blue, Red, Green