Steel Unit Converter — Force, Stress, Moment & Inertia

This is a structural-engineering unit converter — not a generic length-and-weight tool. It covers the five quantities that actually appear on a steel drawing and in a design check, and it groups the units the way an engineer thinks about them:

• Force — axial loads, point loads and reactions: kN, N, kgf, tf (metric ton-force), kip, lbf.
• Stress / pressure — yield strength fy, bending stress σ, bearing pressure: MPa, N/mm², kPa, ksi, psi, kgf/cm².
• Moment / torque — bending moment M, torsion, connection demand: kN·m, N·m, kgf·m, tf·m, kip·ft, lbf·ft, kip·in.
• Line load — uniform / distributed load along a member: kN/m, N/m, kgf/m, tf/m, plf (lb/ft), klf (kip/ft).
• Second moment of area (I) — cross-section stiffness: cm⁴, mm⁴, m⁴, in⁴.

Two things make it different from Omni, RapidTables or UnitConverters.net. First, it keeps the legacy metric units — kgf, tf, kgf/cm², kgf·m — that Anglo-centric tools drop but that dominate Brazilian, Latin-American and older European practice, alongside the modern SI and the full US-customary family. Second, and this is the real point: when you finish a conversion, the value doesn't just sit there. Each category hands the converted number straight to the correct CalcSteel calculator — a force becomes a point load on a beam, a line load becomes a uniform load, a moment opens the shear-and-moment diagram, a stress seeds the buckling check, an inertia opens the profile finder. You go from "what is 30 kip in kN" to "design the beam" in one click.

The result you see the instant the page loads — 100 kN across all six force units — is pre-solved: no button, no login, no watermark.

1. Pick a quantity from the five cards — Force, Stress, Moment, Line Load or Second Moment. The whole unit family for that quantity loads at once.
2. Type a value and choose its unit in the Convert from box. Every other unit updates live in the table below — you never pick a single "to" unit, you see them all (SI and US, tagged so you can tell them apart at a glance).
3. Click any row to re-pivot onto that unit: the same physical quantity, now expressed from that unit, so you can chain conversions without retyping.
4. Copy any value with the little clipboard icon — it copies the number with its unit (e.g. 22.48 kip) so it pastes cleanly into a report or an email.
5. Set the design code. The doctrine bar picks NBR 8800, AISC 360 or EN 1993 (with its steel grade) and a metric⇄US toggle — this decides which grades a stress is matched to and the resistance factor behind the σ = M/Sx utilization.
6. Read the norm-aware result. The panel on the right doesn't just show a number: a stress names its steel grade, a moment shows σ and a code utilization on a profile you choose, an inertia names the nearest real profile from the 1,309-profile catalog.
7. Route it into a calculator — parametrically. Set your span and section and the converted value drives a real FEM beam (point load, UDL or the span/UDL that produces a moment); click through and the calculator opens with your case already solved.
8. Export. Download the whole table as CSV or PDF — free, no watermark, no login.

Tip: the units are exact by definition, so round-tripping (kN → kip → kN) returns your original value to full precision — handy when you are reconciling a US spec against a metric one.

Every factor below is an exact standard definition, not a rounded handbook value. The converter stores each unit as "how many SI base units one of it equals" and converts through that base, so a chain of conversions never accumulates error.

Force (base = newton, N). 1 kgf = 9.80665 N, 1 lbf = 4.4482216152605 N, 1 kip = 1000 lbf:

From	kN	kgf	kip	lbf
1 kN	1	101.972	0.224809	224.809
1 kgf	0.00980665	1	0.00220462	2.20462
1 kip	4.44822	453.592	1	1000
1 tf	9.80665	1000	2.20462	2204.62

Stress (base = pascal, Pa = N/m²). Note 1 MPa ≡ 1 N/mm² exactly, and 1 ksi = 6.894757 MPa:

From	MPa	ksi	psi	kgf/cm²
1 MPa	1	0.145038	145.038	10.1972
1 ksi	6.89476	1	1000	70.3070
1 kgf/cm²	0.0980665	0.0142233	14.2233	1

Moment / torque (base = N·m). 1 kip·ft = 1.3558179 kN·m, 1 kip·ft = 12 kip·in:

From	kN·m	kgf·m	kip·ft	kip·in
1 kN·m	1	101.972	0.737562	8.85075
1 kip·ft	1.35582	138.255	1	12
1 tf·m	9.80665	1000	7.23301	86.7961

Line load (base = N/m). 1 plf = 14.5939 N/m, 1 klf = 1000 plf:

From	kN/m	kgf/m	plf	klf
1 kN/m	1	101.972	68.5218	0.0685218
1 plf	0.0145939	1.48816	1	0.001
1 klf	14.5939	1488.16	1000	1

Second moment of area (base = mm⁴). 1 in⁴ = 25.4⁴ mm⁴ = 41.6231 cm⁴:

From	cm⁴	mm⁴	m⁴	in⁴
1 cm⁴	1	10,000	1×10⁻⁸	0.0240251
1 in⁴	41.6231	416,231	4.16231×10⁻⁷	1
1 m⁴	1×10⁸	1×10¹²	1	2.40251×10⁶

Most unit-conversion mistakes in structural work are not arithmetic — they are category confusions. Watch for these:

• kgf is a force, kg is a mass. 1 kgf = 9.80665 N is the weight of one kilogram under standard gravity. This converter's Force card gives kgf (force); if you meant mass, that is a different quantity. Old drawings and Latin-American practice quote loads in kgf and tf (ton-force = 1000 kgf) — those are forces, and they belong here.
• lbf vs lb (lbm), kip vs klb. In US steel practice "kip" = 1000 pound-force and is unambiguous; "lb" on a load is pound-force too. Do not multiply by g a second time.
• MPa ≡ N/mm². They are the same unit — 1 megapascal is exactly one newton per square millimetre. Seeing both on a datasheet does not mean two different numbers. That is why the converter lists them with identical values.
• Moment unit order matters: kip·ft and kip·in differ by a factor of 12; a value read as kip·in but treated as kip·ft is off by 12×. AISC connection tables usually use kip·in; beam tables usually kip·ft.
• cm⁴ vs in⁴ is a 4th-power conversion: 1 in⁴ = 25.4⁴ mm⁴, so the factor is ≈ 41.62, not 25.4. Length-to-the-fourth conversions are where hand calculations most often slip a decimal.
• kgf/cm² ≈ 0.0981 MPa, and it is almost 1 bar / 1 atm — but not exactly. For fy this matters: an old spec of "2500 kgf/cm²" is 245.2 MPa, not 250.

The converter's colour-coded SI / US tags on every row exist precisely so you never grab a US value where a metric one belongs.

Converting a unit is almost never the goal — it is a step on the way to a design decision. You convert 30 kip to kN because you are about to put that force on a beam; you convert 250 MPa to ksi because you are checking a section against a US spec; you convert a moment to kN·m because you need to size a member for it. A converter that stops at the number makes you copy it, open another tool, and retype it.

This one closes that loop — and, crucially, it does the first slice of the calculation for you before you even leave the page, under an explicit design code you pick (NBR 8800, AISC 360 or EN 1993, shown as a badge with a metric⇄US toggle):

• Stress → a real steel grade. The converted value is matched to the nearest grade of the active code — 250 MPa is A36 / MR250, 345 MPa is A992 / AR350, 355 MPa is S355 — with fy shown in both MPa and ksi, then handed to the column-buckling check as fy.
• Moment → σ = M/Sx with a utilization. Pick a real profile and the tool computes the elastic bending stress and the code utilization η = σ / (fy·φb or fy/γ) inline, and tells you the lightest catalog section that carries the moment — before routing you to the shear-and-moment diagram driven by a span/UDL that reproduces it.
• Inertia → a named profile. "I ≈ 8356 cm⁴" is resolved against the live 1,309-profile database to the nearest real section — "→ IPE 300" — linked straight to its profile page, not just to a finder.
• Force / Line load → a parametric FEM beam. Your converted value becomes a point load or a UDL on a beam of your span and your section (not a hardcoded 6 m IPE 300) — the value is the real driver of the FEM solve, which returns shear, moment and deflection in one click.

And when you just need the numbers, export the whole table as CSV or PDF — free, no watermark, no login. That is the difference between a lookup table and an engineering workflow.

All conversions run through a single SI base per quantity, using these exact primitive constants:

• Standard gravity g = 9.80665 m/s² (defines kgf and tf);
• 1 lbf = 4.4482216152605 N (defines kip, lbf, psi, ksi, plf, klf, kip·ft, lbf·ft, kip·in);
• 1 foot = 0.3048 m and 1 inch = 25.4 mm (defines the length-based US units);
• 1 kgf/cm² = 9.80665 / (0.01 m)² Pa = 98,066.5 Pa.

Because everything is defined (not empirically rounded), the converter is exact to double-precision floating point: a full round-trip through any pair of units in a category returns the input to ~15 significant figures — this is checked programmatically over every unit pair in all five categories. Displayed values use adaptive precision (more decimals for small numbers, scientific notation beyond 10⁷ or below 10⁻⁴) so a stiffness in m⁴ and a stiffness in mm⁴ both read cleanly.

The one thing a converter cannot do for you is decide which quantity you have. kgf is a force; kg is a mass; MPa is a stress; kN·m is a moment; kN/m is a line load. Pick the right card and the numbers are guaranteed correct.