Thread Pitch Converter
Convert threads per inch (TPI) to metric thread pitch in millimeters and back.
How to Use the Thread Pitch Converter
Enter threads per inch (TPI) or metric thread pitch and convert between the two. The relationship is based on 25.4 millimeters per inch.
Practical Example
A 20 TPI thread has a metric pitch of 1.27 mm because 25.4 ÷ 20 = 1.27.
Factors That Affect Thread Selection
Thread standard, diameter, tolerance class, thread form and intended load all matter in addition to pitch.
Frequently Asked Questions
How do I convert TPI to millimeter pitch?
Divide 25.4 by the TPI value.
Is pitch the same as thread diameter?
No. Pitch is the spacing between threads; diameter is a separate dimension.
Can two threads have the same pitch but be incompatible?
Yes. Diameter, thread form and tolerance can still differ.
Understanding Thread Pitch Conversions
Thread pitch can be stated as distance between threads in millimetres or as threads per inch (TPI). The relationship is inverse: metric pitch in millimetres is approximately 25.4 ÷ TPI.
A matching pitch does not guarantee two fasteners are compatible. Thread diameter, profile, angle, handedness and standard must also match, so use the conversion for comparison rather than as the only fit criterion.
Conversion Method and Practical Limits
Threads per inch and metric pitch describe the same spacing inversely: metric pitch in millimeters is 25.4 divided by TPI. Matching pitch alone does not guarantee thread compatibility because diameter, thread form and angle must also match.