Building & DIY

Pitch Diameter Calculator (Gears and Threads)

Find the pitch diameter for a gear from its teeth and pitch, or for a screw thread from its major diameter. It handles both imperial diametral pitch and metric module.

How to use
  1. Pick a mode: gear by diametral pitch, gear by module, or thread.
  2. Enter the tooth count and pitch, or the thread major diameter and pitch.
Estimates only, allow for waste and confirm against local building codes and supplier specs.
Was this helpful?

Common questions

How do I calculate gear pitch diameter?

Divide the number of teeth by the diametral pitch. A 40-tooth gear at 10 DP has a 4-inch pitch diameter.

What is thread pitch diameter?

It is the diameter where thread thickness equals the gap, found as d₂ = d − 0.6495 × P for ISO threads.

Related calculators
From the blog

Guides & how-tos

All articles →
Dates & Time How Banks and Courts Count Days: Business Days, Deadlines & the Fine Print

Institutions don't count days like a calendar. Here's how business days, T+1 stock settlement, bank check holds, and court deadlines under FRCP Rule 6 actually count time, plus the difference between "within X days" and "by the Xth."

· 8 min read Building & DIY How Much Concrete Do I Need for a Slab? (Bags & Yards)

Multiply length by width by thickness in feet, divide by 27 for cubic yards, then add 10% waste. Here's the formula, a slab-size-to-yards-and-bags table, and when to order ready-mix instead of bagging it.

· 7 min read Unit Converters How Many Ounces Are in a Cup? (US vs Metric vs UK)

A US cup holds 8 fluid ounces (236.6 mL), but the legal cup is 240 mL, the metric cup 250 mL, and the old UK cup 284 mL. Here's the full table, a quick fl-oz-to-cups chart, and the fluid-vs-weight-ounce trap that ruins recipes.

· 6 min read