Thread Calculator
Calculate metric, Unified and ACME thread geometry, convert pitch and TPI, or estimate cross-stitch and needlepoint thread.
Calculate ISO metric and Unified screw-thread basic geometry, ACME basic dimensions, thread pitch/TPI and depth, or estimate cross-stitch and needlepoint floss requirements.
Thread result
This thread calculator separates two very different meanings of “thread.” Engineering modes calculate screw-thread pitch and basic geometry. Craft modes estimate how much stranded embroidery floss a cross-stitch or needlepoint project may use.
Screw Thread Calculator
The screw-thread modes work from nominal major diameter and pitch. For metric threads, pitch is entered directly in millimetres. For Unified and ACME threads, pitch is calculated from threads per inch:
Pitch (in) = 1 ÷ TPI
For multiple-start threads, lead = pitch × number of starts. The calculator also reports an approximate lead angle at the basic pitch diameter.
Metric Screw Thread Calculator
The metric screw thread calculator uses the 60° ISO metric basic/design-profile relationships associated with ISO 68-1 and ISO 724. For nominal major diameter d and pitch P:
Fundamental triangle H = 0.8660254P
Basic pitch diameter d2 = d − 0.649519P
External root/reference diameter d3 = d − 1.226869P
Internal basic minor diameter D1 = d − 1.082532P
The external radial reference depth is about 0.613435P. These are basic/reference dimensions, not finished inspection limits. ISO 965 tolerance classes and fundamental deviations determine allowable manufactured sizes.
Unified Screw Thread Calculator
The Unified inch mode uses the same 60° geometric constants after converting TPI to pitch. It reports basic pitch diameter, a flat-root external reference diameter, the internal basic minor diameter, reference depth, lead and lead angle. Real UNC/UNF/UN parts require the correct ASME B1.1 class allowances and tolerances.
ACME Thread Calculator
The ACME thread calculator covers the General Purpose 29° basic form described by ASME B1.5. For pitch P and nominal major diameter D:
Basic depth = P/2
Basic pitch diameter = D − P/2
Basic minor diameter = D − P
Basic crest flat ≈ 0.3707P
Actual 2G, 3G and 4G limits add allowances, clearances and tolerances. The calculator deliberately does not present basic dimensions as inspection limits.
Thread Pitch Calculator and Depth of Thread Calculator
The pitch/depth mode converts between metric pitch and TPI and gives a reference radial depth for a 60° external profile, 60° internal profile or ACME basic profile. This is useful when you know only pitch or TPI and want a quick thread pitch calculator or depth of thread calculator.
Cross Stitch Thread Calculator
The cross stitch thread calculator estimates skein usage for one floss color from full-cross stitch count, fabric count, number of strands and a safety allowance. DMC states that its standard Six-Strand Embroidery Floss is sold in 8 m / 8.7 yd skeins with six separable strands.
Because real stitching paths vary, the calculator uses a practical planning baseline of about 1,700 full crosses per 8 m skein at 14-count with two strands, then scales capacity in proportion to fabric count and inversely with the number of strands. Add a waste allowance for tails, starts, stops, unpicking and personal tension.
Needlepoint Thread Calculator
The needlepoint thread calculator uses canvas mesh to estimate the geometric diagonal distance of each stitch, applies a planning factor for half-cross, continental or basketweave tent stitch, multiplies by the number of plies, and compares total strand length with the 48 strand-metres available in an 8 m six-strand skein.
Decorative stitches, compensation at shape edges, heavy coverage, painted canvas and individual tension can shift real consumption. For expensive fibers or large projects, stitch a measured sample first.
Frequently Asked Questions
Is thread pitch the same as TPI?
They describe the same spacing in different ways. In inch units, pitch is 1/TPI. For metric pitch in millimetres, TPI equivalent is 25.4/pitch.
What is the depth of an ISO metric external thread?
The external radial reference depth used here is approximately 0.613435 times pitch. Actual root geometry and tolerance limits depend on the applicable ISO design profile and tolerance class.
What angle is an ACME thread?
General Purpose ACME threads use a 29° included angle. This is different from the 60° profile used by ISO metric and Unified fastening threads.
Can I use basic thread dimensions for machining inspection?
Not by themselves. Basic geometry is the starting profile. Production parts require the correct standard, tolerance class, allowances, gage method, coating allowance and other drawing requirements.
How many strands are in a DMC embroidery floss skein?
DMC describes its standard cotton embroidery floss as six-strand floss sold in 8 m / 8.7 yd skeins. Stitchers separate the bundle and use the number of strands required by the pattern and fabric.
Methodology and Sources
Metric screw-thread standard scope is cross-checked against ISO 68-1:2023 and ISO 724:2023. ACME scope and the current reaffirmed B1.5 standard are cross-checked against ASME. Embroidery-floss length and strand count are cross-checked against DMC product specifications. Craft usage is an estimating model rather than a manufacturer guarantee.