Thread Pitch
Calculate thread pitch in mm and inches from thread length and number of threads or from TPI. Free thread pitch calculator for metric and imperial threaded fasteners with charts.
About This Calculator
Our free online Thread Pitch Calculator helps engineers, machinists, DIY enthusiasts, and anyone working with threaded fasteners to quickly determine the thread pitch of bolts, screws, and other threaded components. Whether you are identifying an unknown fastener, designing threaded connections, or verifying thread specifications, this calculator provides instant and accurate results for both metric and imperial threads.
The thread pitch is calculated using the simple formula: P = L / n, where P is the thread pitch, L is the total length of the threaded portion, and n is the number of threads along that length. The calculator also computes the Threads Per Inch (TPI) value and provides the pitch in both millimeters and inches for maximum flexibility. For imperial threads, you can also enter the TPI directly to determine the thread pitch.
Thread pitch is a fundamental specification in mechanical engineering and manufacturing. It determines how far a threaded fastener advances with each rotation and directly affects the strength, thread engagement length, and torque requirements of bolted connections. ISO metric threads use the pitch in millimeters (e.g., M10 × 1.5 means a 10 mm diameter bolt with 1.5 mm thread pitch), while unified threads use TPI (e.g., 3/8-16 UNC means 16 threads per inch).
How to Measure Thread Pitch
For metric threads, simply measure the distance between two adjacent thread crests using a ruler or caliper on the millimeter scale. For imperial threads, count how many threads fit within one inch and divide 1 by that number. A thread pitch gauge is the most accurate tool, with toothed shims that match standard thread profiles for quick identification.
Regional Notes
Thread pitch standards are used globally. Most countries use ISO metric thread standards (pitch in mm), while the United States primarily uses the Unified Thread Standard (UTS) with TPI values. The United Kingdom uses both metric and imperial threads depending on the application. This calculator supports all systems by showing the pitch in both mm and inches along with the TPI value.
Frequently Asked Questions
What is thread pitch?
Thread pitch is the distance between the same point on two adjacent threads of a threaded fastener, such as a bolt or screw. It is typically measured from crest to crest or root to root of consecutive threads.
How do I calculate thread pitch from length and number of threads?
To calculate thread pitch, divide the total thread length by the number of threads along that length. For example, if a bolt has 10 threads over a 25 mm length, the thread pitch is 2.5 mm. Use the formula: P = L / n where P is pitch, L is thread length, and n is the number of threads.
What is the difference between thread pitch and TPI?
Thread pitch is the distance between adjacent threads (measured in mm or inches), while TPI (Threads Per Inch) is the number of threads in one inch of length. They are reciprocals: P = 1 / TPI (in inches). For metric threads, pitch in mm is specified, while imperial threads use TPI.
What are standard metric thread pitches?
Standard metric thread pitches for ISO coarse threads range from 0.2 mm for very fine threads up to 6.0 mm for large threads. Common pitches include 0.5, 0.8, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 mm. Each diameter has a standard coarse and fine pitch.
How do I convert thread pitch between metric and imperial?
To convert metric thread pitch (mm) to imperial, divide by 25.4 to get inches. To find TPI, divide 25.4 by the pitch in mm. For example, a 1.5 mm pitch equals 0.059 inches or approximately 16.9 TPI. Conversely, 20 TPI equals a pitch of 0.05 inches or 1.27 mm.
What tools can I use to measure thread pitch?
Thread pitch can be measured using a ruler or caliper by measuring the distance between two thread crests. A thread pitch gauge set provides toothed shims that match the thread profile for precise identification. For digital measurement, calipers and pitch gauges offer the most accurate results.
How do I measure thread pitch with a ruler?
To measure thread pitch with a ruler, align a thread crest with the zero mark on the ruler and measure the distance to the next crest. For metric threads, use the millimeter scale. For imperial threads, count how many threads fit within an inch, then divide 1 by that number to get the pitch in inches.
How do I use this thread pitch calculator?
Enter the thread length in millimeters and the total number of threads along that length to calculate the thread pitch. Alternatively, switch to TPI mode and enter the threads per inch value directly. The calculator instantly displays the pitch in mm and inches plus the TPI value, with an optional chart comparing standard metric pitches.