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Construction Calculators

Thread Pitch Calculator

Convert a screw or bolt's threads-per-inch (TPI) rating to metric thread pitch in millimeters, or the reverse, and estimate thread depth.

Example: a 1/2-13 UNC bolt has 13 threads per inch.
mm
Example: an M12 x 1.75 metric bolt has a pitch of 1.75mm.
Threads per inch (TPI) —
Thread pitch —
Thread pitch —
Basic thread depth (60° form) —
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About the Thread Pitch Calculator

Thread pitch describes the spacing between adjacent threads on a screw or bolt. Imperial fasteners are specified by threads per inch (TPI), while metric fasteners are specified by pitch directly in millimeters — this calculator converts between the two and estimates the basic thread depth for a standard 60° thread form.

Formula: Pitch (in) = 1 ÷ TPI; Pitch (mm) = Pitch (in) × 25.4; TPI = 25.4 ÷ Pitch (mm); Thread Depth ≈ 0.613 × Pitch (the standard basic height for 60° Unified and ISO metric thread forms)

Use this when matching a mystery fastener to a tap, die or nut, or when substituting a metric bolt for an imperial one (or vice versa). Thread depth is a theoretical value based on a sharp-V 60° thread profile — real UNC/UNF and ISO metric threads are slightly truncated at the crest and root, so actual engagement depth is a bit less than this calculated figure.

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