Screw Lead and Pitch Calculator

How it is calculated

The tool multiplies the thread pitch by the number of thread starts: lead = pitch × starts. Pitch is the distance between neighbouring thread crests in millimetres. Lead is how far the screw or nut advances in one full turn, and it is shown in millimetres with two decimals. For a single-start thread lead and pitch are equal. A second line repeats the pitch you entered, rounded to two decimals. Pitch must be above zero and starts must be a whole number of at least 1: 0, or a fraction such as 2.5, gives no result, just as a real thread cannot have half a start. The tool converts nothing from inches, so a thread given in threads per inch must be converted to a pitch in millimetres first.

Common mistakes

• Using lead and pitch as if they were the same on a multi-start screw. A 2 mm pitch with 4 starts advances 8 mm per turn, not 2 mm.
• Entering the lead into the pitch field. The tool would then multiply it by the starts again and report a lead that is several times too high.
• Typing threads per inch as the pitch. A thread of 10 threads per inch has a pitch of 2.54 mm, which is 25.4 ÷ 10, and typing 10 gives 10 mm.
• Entering a fractional number of starts such as 2.5. The tool shows no result because a real thread cannot have half a start.
• Counting the grooves visible along the length instead of the starts. The number of starts is how many separate thread ends you see at the screw tip.