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.

Thread Dimension Calculator

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.

Page last changed 2026-10-19 · 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

Major diameter (inch)

Threads per inch

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.

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

#	Source	Type	Revision / method
[1]	ASME B1.1 — Unified Inch Screw Threads (UN and UNR Thread Form)	reference	ASME B1.1-2019 — source
[2]	Values computed in your browser	derived	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

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

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. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. 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

Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "Thread Dimension Calculator." https://refmanual.com/calculators/thread-dimensions/ (accessed 2026-10-19). Data from ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019.

BibTeX

@misc{thread-dimensions,
  title        = {Thread Dimension Calculator},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/calculators/thread-dimensions/}},
  note         = {Accessed: 2026-10-19},
  source       = {ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Thread Dimension Calculator
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/calculators/thread-dimensions/
PY  - 2026
DA  - 2026-10-19
N1  - Source: ASME B1.1 — Unified Inch Screw Threads, ASME B1.1-2019
ER  -