Gear Span Calculator

This calculator provides size measurements for gears based on measuring across a number of teeth (spanning these teeth). Rather than measuring across the entire gear, like with Measurement over Pins, span measurements use calipers to measure across a fixed number of gear teeth. As gears grow larger, the span measurement may be easier for an operator, and doesn't require giant calipers.

Input your gear parameters to find the acceptable range for the number of teeth to measure over, choose your number, then calculate the correct measurement to check out your gear.
Results conform to ANSI/AGMA 2002-D19 published in December 2019


The default Manufacturing Profile Shift Coefficient is 0. Positive values result in thicker teeth, as if your cutting tool did not cut to a full depth, while negative values result in thinner teeth.

When designing a gear system, it's important to know the how far apart your two gears should be. Using a Center Distance Calculator ensures the proper mesh between gears by providing the ideal distance between between the centers of two spur gears.

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Using an involute gear cutter to mill a gear

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Calculating Span Measurement of Gear Teeth

Measuring the teeth on a gear is essential to ensuring it's the correct size and will mesh correctly with its mate. However, as the gear size increases it can become more difficult to reliably measure across the full diameter of the gear (and the necessary tools get even more expensive!)

The gear span measurement allows you to measure across a limited number of teeth, using smaller and simpler tools (like basic micrometers and calipers)

How to Measure Gear Teeth

Gear span measurement is easiest to perform with a caliper or micrometer that can "reach" into the spaces between the gear teeth. Make sure your tool comes in radially (as shown in the picture) so the two points of contact with the gear teeth are on the same imaginary circle. The key is to ensure you aren't deep on one tooth and near the edge on the second.

Gear Span Measurement Chart

Gear span measurements depend on the: total number of teeth, pitch of the gear, pressure angle, profile shift, and the number of teeth you intend to span. As a result, a generic gear span measurement chart isn't too practical; the image below shows just the combinations for a 20-tooth metric gear, spanning 3 teeth. Considering the near infinite possibilities, we would recommend using the calculator to make your own gear span measurement charts to fit your specific application

Gear Span Measurement:

› Input gear parameters

› Choose how many teeth you want to measure across

› Calculate ideal span dimension