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Engineering Unit Converter

Convert between engineering units instantly: length, area, force, pressure, moment, mass, temperature and angle - built for structural and civil engineering calculations.

Free online calculator with step-by-step working and one-click Excel (.xlsx) and PDF export.

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Using this engineering unit converter

What it converts

This converter covers the quantities that appear in structural and civil engineering calculations: length, area, volume, mass, force, pressure and stress, moment, density, temperature, and the section properties - second moment of area and section modulus - whose powers make them the easiest to get wrong.

It works between SI, metric-technical (kgf-based) and US customary units in both directions, which is the case that matters when reading an AISC table alongside a Eurocode calculation.

The conversions that actually cause errors

Most unit mistakes in structural work are not exotic. They come from a small set of traps, and the powers are the worst of them:

Stress identity worth memorising
1 MPa = 1 N/mm2 exactly
Second moment of area
1 cm4 = 10 000 mm4 (10^4, not 10^2)
Section modulus
1 cm3 = 1000 mm3
Area
1 cm2 = 100 mm2
Force from mass
1 kgf = 9.80665 N
Imperial stress
1 ksi = 6.894757 MPa
Imperial moment
1 kip-ft = 1.355818 kNm
Imperial length
1 inch = 25.4 mm exactly

The section-property powers are the single most common source of a wrong answer by a factor of ten thousand. Section tables quote second moment of area in cm4 and section modulus in cm3 while most calculations run in mm, so the conversion is 10^4 and 10^3 rather than the 10^1 that intuition suggests from cm to mm. A deflection that comes out ten thousand times too large is almost always this.

The other frequent trap is treating kgf and N as interchangeable. A load quoted in kg is a mass; the force it applies is that mass times 9.80665. In older Vietnamese and Russian practice loads are often tabulated in kgf or tf, and mixing those directly into a Eurocode calculation understates the force by an order of magnitude.

Assumptions and limits

Conversions use the internationally defined factors - the inch is exactly 25.4 mm and standard gravity is exactly 9.80665 m/s2 by definition, so those are not approximations. Values are converted at full precision and rounded only for display, so a round-trip conversion returns the original number.

The converter handles units, not quantities that need physical context. Converting a stress is unambiguous; converting a "load" quoted in kg requires knowing whether it is a mass or a force already expressed as kgf, and the tool cannot tell which you mean. Temperature differences and absolute temperatures also convert differently - a 10 degree Celsius rise is a 10 kelvin rise but not 283 K.

FAQ

Yes, exactly - they are identical by definition, since 1 Pa is 1 N/m2. Eurocode writes concrete and steel strengths in N/mm2 and most software reports MPa; no conversion is needed between them.

Ten thousand. The conversion is 10^4 because it is a fourth power of the 10 mm in a centimetre, not 10 or 100. Getting this wrong is the most common cause of a deflection that is out by orders of magnitude.

No - kg is mass, kgf is force. 1 kgf = 9.80665 N. Older tables and some regional practice quote loads in kgf or tonne-force, and treating those numbers as newtons understates the force roughly tenfold.

A thousand pounds force, used throughout AISC and US practice. 1 kip is 4.448222 kN, and 1 kip-ft is 1.355818 kNm.

Because the numbers are a convenient size - an IPE 300 has 8356 cm4 rather than 83 560 000 mm4. It is a presentation convention, and it is exactly why the power-of-ten conversion has to be done carefully when the calculation itself runs in mm.

Absolute temperatures convert with the offset (0 Celsius is 273.15 K). A temperature difference does not - a rise of 10 degrees Celsius is a rise of 10 K. For thermal expansion you want the difference, so make sure you are converting the right one.

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