Engineering Reference

Unit Converter

Convert between the units engineers actually use — length, pressure, force, torque and temperature — with the exact factors.

Data verified 2026-09-29 · based on n/a — standard engineering relationships, no single governing revision

Quick Answer

Enter a value in any field and the others update. Length uses 25.4 mm per inch exactly; pressure uses 1 psi = 6.894757 kPa; temperature is the only one that needs an offset, not just a factor.

Unit Converter

The Formulas Used

Length 1 in = 25.4 mm (exact) · Pressure 1 psi = 6.894757 kPa
Torque 1 lb·ft = 1.355818 N·m · Force 1 lbf = 4.448222 N
Temperature is the exception: °F = °C × 9/5 + 32 — an offset as well as a factor.

Temperature Is Different

Every other conversion on this page is a pure multiplication, because the units share a zero point. Temperature scales do not — 0 °C and 0 °F are different temperatures — so a conversion needs both a factor and an offset.

This matters when converting temperature differences: a change of 1 °C equals a change of 1.8 °F, with no offset. Mixing the two up is a common source of error in thermal expansion and heat transfer work.

Where the Factors Come From

The length and mass conversions are exact by definition — the inch has been defined as exactly 25.4 mm since 1959. Pressure and torque conversions are derived from those plus the standard gravity definition, so they carry more decimal places than are usually needed.

Frequently Asked Questions

How many mm in an inch?
Exactly 25.4. The inch has been defined as 25.4 mm since 1959, so the conversion is exact and not subject to rounding.
How do I convert psi to bar?
Multiply by 0.068948, or divide by 14.50377. 100 psi is 6.895 bar, and 1 bar is 14.504 psi.
How do I convert Nm to lb-ft?
Multiply by 0.737562. 10 N·m is 7.376 lb·ft, and 1 lb·ft is 1.356 N·m — the two units differ by about 36%.
Why is temperature conversion different?
Because the scales have different zero points. Converting between °C and °F needs an offset as well as a factor, unlike length or pressure where both scales share a zero.
How do I convert a temperature difference?
Multiply by 1.8 only — no offset. A rise of 10 °C is a rise of 18 °F. Adding the 32 is the common mistake here.

Related

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#SourceTypeRevision / method
[1]ASME B1.1 — Unified Inch Screw ThreadsstandardASME B1.1-2019 — source
[2]ASTM A615 — Deformed steel bars for concrete reinforcementstandardASTM A615/A615M-20 — source
[3]ASTM E140 — Hardness Conversion TablesstandardASTM E140-12b — source
[4]Values computed in your browserderivedEvaluated locally from the formulas shown on the page. No data leaves the device.
[5]ISO 4287 — Surface texture: Profile methodstandardISO 4287:1997 — source
[6]ISO 68-1 — Basic profilestandardISO 68-1:2023 — source
[7]NFPA 70 NEC Table 310.16standardNEC 2023 (NFPA 70-2023) — source

Data Sources

StandardRevisionWhat it covers on this page
Formulas as shown on this pagen/a — standard engineering relationships, no single governing revisionevery value this calculator produces

Cross-checked against:

Derived values — the following values on this page are calculated, not taken directly from the standard:

ValueHow it is derived
All outputsComputed in the browser from the formulas above. No data leaves the device.

Outputs are computed from the formulas shown. Verify against the governing standard for design or acceptance work.

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.