Enter a nominal diameter and a pitch to compute every basic dimension of a 60° thread form — the same formulas used to generate the thread charts on this site.
Data verified 2026-09-29 · based on ASME B1.1-2019
Quick Answer
Enter the nominal major diameter and the threads per inch. The calculator applies the ASME B1.1 basic profile: d2 = d − 0.75H, d1 = d − 2(0.61343P) and As = π/4 × (d − 0.9743/n)².
Calculate Thread Dimensions
The Formulas Used
P = 1 / n H = (√3 / 2) × P d2 = d − 0.75H basic pitch diameter d1 = d − 2(0.61343P) external minor diameter D1 = d − 2(0.54127P) internal minor diameter As = (π/4) × (d − 0.9743/n)² tensile stress area
where d is the nominal major diameter in inches, n is threads per inch and P is the pitch in inches. These are the ASME B1.1 basic-profile relationships.
The metric series uses a different stress-area formula. ISO 898-1 uses As = (π/4) × (d − 0.9382P)² with dimensions in millimetres. The coefficients differ because the two standards reference different minor diameters — do not mix them.
What These Dimensions Are For
Pitch diameter (d2) controls assembly and is what a thread micrometer or thread comparator measures. A thread can meet its major and minor limits and still not fit if d2 is wrong.
External minor diameter (d1) sets the root of a bolt thread and therefore its fatigue behaviour — a sharper root performs worse.
Internal minor diameter (D1) is the bore a tap must clear, and drives tap drill selection and tapping torque.
Tensile stress area (As) is the effective area used for bolt strength. It is not the nominal circle area — using the nominal diameter overstates capacity by roughly a third.
Basic Dimensions vs Limit Dimensions
Everything this calculator produces is a basic dimension — the theoretical profile with no allowance or tolerance applied. A production thread is specified by class of fit (2A/2B or 3A/3B for inch, 6g/6H for metric) and the acceptable limits derive from that class.
A calculator of this kind is useful for checking proportions, sizing a tap drill, or verifying a chart. It is not a substitute for the limit dimensions in the standard when an assembly has to pass inspection.
Frequently Asked Questions
How is the tensile stress area calculated?
For unified inch threads, As = π/4 × (d − 0.9743/n)², where d is the nominal major diameter and n is threads per inch. Metric threads use As = π/4 × (d − 0.9382P)² per ISO 898-1, with the pitch in millimetres. Both give an area between the pitch diameter and the minor diameter rather than the nominal circle.
What is the pitch diameter and why does it matter most?
It is the diameter at which thread width and groove width are equal. It determines whether an external and internal thread will assemble, which is why inspection gauges and thread micrometers measure it rather than the major diameter.
Can I use this calculator for metric threads?
Not directly — the input is threads per inch. Convert by dividing 25.4 by the metric pitch: 1.5 mm is 25.4 ÷ 1.5 = 16.93 TPI. The stress area shown will then use the unified coefficient, which differs from the ISO 898-1 value by about 2%.
What diameter do I enter — nominal or actual?
The nominal major diameter, for example 0.2500 for a 1/4 in thread. Basic dimensions are derived from the nominal size; entering a measured diameter produces dimensions that correspond to no standard thread class.
The formulas above, evaluated locally. No data leaves the device. The same formulas generate the thread charts on this site.
Data Sources
Standard
Revision
What it covers on this page
ASME B1.1 — Unified Inch Screw Threads
ASME B1.1-2019
the basic profile and stress-area definition used by this calculator
ISO 898-1 — Mechanical properties of fasteners
ISO 898-1:2013
the metric stress-area formula noted above
Cross-checked against:
The calculator's formulas are the same functions that generate the published thread charts, so entering a standard size reproduces the charted values
Spot-checked against the 1/4-20 and M10x1.5 reference values on those pages
Derived values — the following values on this page are calculated, not taken directly from the standard:
Value
How it is derived
All outputs
Computed in the browser from the ASME B1.1 basic profile — see the formulas above.
Outputs are basic dimensions with no class-of-fit allowance. For a threaded assembly, obtain the limit dimensions for the required class from the standard.
Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.
Cite This Page
Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:
Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.
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