Machining

Thread Pitch Calculator

Calculate tap drill sizes, thread percentages, and pitch dimensions.

Input Parameters

Calculate

Threads Per Inch (TPI)

TPI

Results

Enter thread data and click Calculate

What is Thread Pitch?

Thread pitch is the distance between adjacent thread crests, measured in millimeters for metric threads or expressed as Threads Per Inch (TPI) for imperial threads.

Understanding thread pitch is essential for selecting matching fasteners, choosing correct taps and dies, and calculating thread depths and engagement lengths.

How to Use

Select conversion mode: TPI to Pitch, Pitch to TPI, or Thread Dimensions
For TPI/Pitch conversion, enter the known value
For Thread Dimensions, enter major diameter and pitch/TPI
Select the appropriate thread form for accurate calculations
Click Calculate to see results

FAQs

Pitch is the distance between threads in millimeters (metric system). TPI is threads per inch (imperial system). They're inversely related: Pitch (mm) = 25.4 ÷ TPI. For example, 20 TPI = 1.27mm pitch.

Pitch diameter is the theoretical diameter where the thread tooth and groove widths are equal. It's the most important measurement for thread fit - two threads with matching pitch diameters will have proper engagement regardless of minor variations in major/minor diameters.

Use a thread pitch gauge to find the pitch or TPI. Measure major diameter with calipers. For imperial threads, check if TPI matches standard UNC/UNF series. For metric, common pitches are 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0mm. If nothing matches, it may be a pipe thread or specialty thread.

Coarse threads (UNC, standard metric) have fewer TPI/larger pitch. They're stronger, easier to assemble, more tolerant of damage, and better for soft materials. Fine threads (UNF, metric fine) have more TPI/smaller pitch. They're better for thin-wall applications, provide finer adjustment, and resist vibration loosening.

Unified/ISO 60° threads are standard for fasteners. ACME 29° threads are for power transmission (leadscrews). Buttress threads handle high axial loads in one direction. Whitworth 55° threads are older British standard, still found on vintage equipment. Always match thread form when replacing fasteners.

Limitations

• Thread dimensions are theoretical values based on standard formulas
• Actual thread geometry varies with manufacturing tolerances
• Does not account for thread class tolerances (2A, 2B, 6g, 6H, etc.)
• Specialty threads may use different depth factors
• Always verify critical dimensions with thread gauges