Thread Calculator — Screw Thread Dimensions
Enter major diameter and pitch (or TPI) to get pitch diameter, minor (root) diameter, thread depth, lead angle and tap-drill size for ISO metric or unified UNC/UNF threads.
Thread standard
mm
mm
Diameter where thread width equals thread space — governs fit class
- 1
Fundamental triangle height
H = (√3 ÷ 2) × 1,5 = 1,299H is the height of the sharp 60° thread-profile triangle for pitch P. - 2
Pitch diameter
10 − (3 ÷ 4) × 1,299 = 9,0257
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For 60° threads: H = (√3/2)P. Pitch Ø = D−(3/4)H (both standards). Metric minor Ø = D−(5/4)H ≈ D−1.0825P; unified minor Ø = D−(3/2)H ≈ D−1.2990P. Thread depth per side = (D−minor)/2. Metric tap drill ≈ D−P. For unified, use the calculated minor diameter to select the nearest standard drill.
Formel
How this is calculated
Both ISO metric and unified (UNC/UNF) screw threads use a 60° included angle and share the same fundamental geometry, differing only in units and root form. The fundamental triangle height for a 60° thread is H = (√3/2)×P, where P is the pitch (distance between adjacent crests in mm for metric, or 1/TPI in inches for unified).
Three key diameters define the thread: major diameter D is the outer crest diameter (the nominal "size" stamped on the bolt or nut); pitch diameter = D − (3/4)H is where thread width equals thread space — it governs the fit class (how loose or tight the mating threads are); minor (root) diameter is the core of the bolt or crest of the nut, which differs between standards. ISO metric threads have rounded roots, giving minor Ø = D − (5/4)H ≈ D − 1.0825P. Unified threads have flat roots, giving minor Ø = D − (3/2)H ≈ D − 1.2990P. Thread depth (radial, per side) = (D − minor Ø) / 2.
The tap drill size shown is the calculated minor diameter — in practice, choose the nearest standard drill size at or slightly above this value to leave enough material for the tap to form the threads. For metric: tap drill ≈ D − P is the widely used rule-of-thumb that gives ≈ 75% thread engagement. This calculator covers single-start threads only; tolerance grades and surface coatings are not modelled.
Vanliga frågor
Pitch diameter is the imaginary cylinder where thread ridge width equals thread groove width — it determines the tolerance class (2A/2B for unified, 6g/6H for metric) and how tightly two mating threads fit. Minor diameter is the root (core) of the bolt; it sets the bolt's tensile stress area and is the key dimension for choosing a tap drill.
Metric shortcut: tap drill ≈ major diameter − pitch (e.g., M10×1.5 → 8.5 mm). Unified shortcut: use the minor diameter from this calculator and pick the nearest standard drill slightly above it (e.g., ½-13 UNC minor = 0.400 in → use 25/64 in = 0.391 in for ~75% thread engagement). Finer threads and harder materials may warrant a drill slightly larger than the minor diameter to reduce tapping torque.
UNC (Unified National Coarse) has fewer threads per inch — faster to assemble, more tolerant of minor damage, better for softer materials. UNF (fine) has more TPI per diameter — higher tensile strength per bolt, better vibration resistance, finer adjustment. Both use identical 60° geometry; only the pitch differs.
Även känt som
TG we-Calculate Editorial Team. (2026). Thread Calculator — Screw Thread Dimensions [Online calculator]. TG we-Calculate. https://we-calculate.com/sv/calculator/thread-calculator
TG we-Calculate Editorial Team. "Thread Calculator — Screw Thread Dimensions." TG we-Calculate. 2026. https://we-calculate.com/sv/calculator/thread-calculator.
TG we-Calculate Editorial Team, "Thread Calculator — Screw Thread Dimensions," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/sv/calculator/thread-calculator
@misc{wecalculate_thread_calculator, title = {Thread Calculator — Screw Thread Dimensions}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/sv/calculator/thread-calculator}}, year = {2026}, note = {TG we-Calculate} }
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