Area times length times density, and nothing else
Metal weight has no complications hiding in it. Work out the cross-sectional area of the profile in square inches, multiply by the length in inches to get cubic inches of metal, and multiply by density in pounds per cubic inch. Everything a weight table contains is that calculation performed once per size.
What varies is the area formula, and there are only a handful worth memorising. A round bar is πD²/4. A square is simply the side squared. A hex bar sized across the flats has area (√3/2) × F² = 0.8660 F², which is why a 1 in hex weighs about 10 percent more than a 1 in round and about 15 percent less than a 1 in square. Flat bar is width times thickness.
Hollow sections are the same idea with a subtraction. A round tube is the outside circle minus the bore, which simplifies neatly to π × t × (OD − t) — a form worth remembering because it needs no squaring at all. A square tube with sharp corners is 4t(B − t). An equal-leg angle is two legs sharing a corner, so t(2L − t) counts the corner once rather than twice.
Density then scales the answer directly. Carbon steel at 0.2836 lb/in³ and 6061 aluminium at 0.0975 lb/in³ differ by a factor of 2.91, so the same profile in aluminium weighs about a third of the steel version. Pick the wrong alloy and the answer is wrong in exactly that proportion — no other input has such leverage.
Densities that matter, and where catalogue weights differ
The densities on this page are the standard values used across the metals trade: 0.2836 lb/in³ for carbon steel (7,850 kg/m³), 0.289 for austenitic stainless, 0.0975 for 6061 aluminium, 0.307 for free-machining brass, 0.323 for copper, 0.160 for Ti-6Al-4V. Small variations exist between grades within a family, but they are well under one percent and swamped by mill tolerance on the section itself.
Two shapes deserve a caveat, because catalogue weights will not exactly match the sharp-corner arithmetic.
Structural angles are hot-rolled with a fillet at the root and radii at the toes. The fillet adds a little material and the toe radii remove a little, and the net effect is that catalogue weights sit slightly above the sharp-corner formula on small sections. The 2 × 2 × 1/4 angle is a useful check: the sharp-corner area is 0.9375 in² giving 3.19 lb/ft, which is the published figure.
Square and rectangular tube made as structural HSS to ASTM A500 has substantial radiused outside corners, conventionally taken as twice the wall thickness. Those corners remove roughly 3(4 − π)t² from the sharp-corner area, which is around 4 percent on a typical section — enough to matter when you are ordering by weight. This calculator uses the sharp-corner form, which suits mechanical tube; use the tube and pipe weight calculator when you need to match an HSS catalogue.
Converting between systems is a matter of two constants. Pounds per foot times 1.48816 gives kilograms per metre. Pounds per cubic inch times 27,680 gives kilograms per cubic metre, which is why 0.2836 lb/in³ and 7,850 kg/m³ are the same statement.
Worked example: ten pieces of 2 in angle
You are quoting ten pieces of 2 × 2 × 1/4 carbon steel angle, each 8 ft long, at a service centre price of $1.20 per pound.
- Cross-sectional area. t(2L − t) = 0.25 × (4 − 0.25) = 0.25 × 3.75 = 0.9375 in².
- Weight per foot. 0.9375 × 12 × 0.2836 = 3.1905 lb/ft, which matches the published 3.19 lb/ft for L2×2×1/4.
- Weight per piece. 8 ft × 3.1905 = 25.524 lb.
- Lot weight. 25.524 × 10 = 255.24 lb.
- Material cost. 255.24 × $1.20 = $306.29.
- Metric check. 3.1905 lb/ft × 1.48816 = 4.748 kg/m.
Now change one thing: the same angle in 6061 aluminium. Density falls from 0.2836 to 0.0975, a ratio of 0.3438, so weight per foot becomes 3.1905 × 0.3438 = 1.0969 lb/ft and the lot drops to 87.75 lb. Aluminium usually costs several times more per pound, so the material cost may still be higher despite the lower weight — which is exactly why quoting from weight alone misleads when comparing alloys.
One more useful comparison from the same numbers. A solid 2 in square bar would be 2² × 12 × 0.2836 = 13.61 lb/ft, more than four times the angle. The angle gets most of the bending stiffness of a much heavier section by putting metal where it does work, which is the entire reason structural shapes exist.
Carbon steel solid bar weight per foot
| Size (in) | Round (lb/ft) | Square (lb/ft) | Hex (lb/ft) | Round (kg/m) |
|---|---|---|---|---|
| 1/4 | 0.167 | 0.213 | 0.184 | 0.249 |
| 1/2 | 0.668 | 0.851 | 0.737 | 0.994 |
| 3/4 | 1.504 | 1.914 | 1.658 | 2.237 |
| 1 | 2.673 | 3.403 | 2.948 | 3.978 |
| 1-1/4 | 4.176 | 5.318 | 4.605 | 6.215 |
| 1-1/2 | 6.014 | 7.657 | 6.632 | 8.949 |
| 2 | 10.692 | 13.613 | 11.790 | 15.911 |
| 3 | 24.057 | 30.629 | 26.528 | 35.798 |
For other alloys, multiply by the density ratio: 0.344 for 6061 aluminium, 1.019 for 304 stainless, 1.082 for brass 360, 0.564 for Ti-6Al-4V.
Errors that show up on the weighbridge
- Measuring hex bar across the corners. Hex stock is sized across the flats. Across the corners is 1.1547 times larger, and squaring that error inflates weight by 33 percent.
- Using nominal pipe size as an outside diameter. Nominal pipe sizes below 14 in are not the outside diameter at all — 2 in NPS pipe is 2.375 in OD. Use the actual measured OD.
- Applying sharp-corner tube formulas to structural HSS. A500 corners are radiused at about twice the wall, which removes roughly 4 percent of the area on typical sections.
- Forgetting saw kerf and drops. Ten pieces at 8 ft need more than 80 ft of stock. Add kerf per cut and the unusable remnant at the end of each length when ordering.
- Carrying the steel density into an aluminium job. The ratio is 2.91, so the mistake nearly triples the answer. It is the largest single error available on this page.
- Confusing mass and force units. A pound-mass and a pound-force are numerically equal at standard gravity but are different quantities; keep them apart when the weight feeds a structural calculation rather than a freight document.
- Ignoring mill tolerance on hot-rolled stock. Sections are supplied to a size tolerance, so an actual weighbridge figure can differ from the calculated one by a percent or two. Purchase orders written by weight normally state the basis.
What the weight number is used for downstream
Weight is the currency of the metals trade. Mills and service centres price nearly everything by the pound or the hundredweight, freight is booked by weight, and cranes and racking are rated by it. Getting the weight right early is what keeps a quote from turning into a loss and a lift from turning into an incident.
For flat material the arithmetic is easier still, and the trade quotes it per square foot rather than per foot of length — the steel plate weight calculator handles plate, sheet and circular blanks, including cut-outs. For hollow round and rectangular sections where you need catalogue-matching numbers, the tube and pipe weight calculator applies the corner correction and also reports internal volume, which matters when the tube will carry fluid.
Weight also feeds fabrication planning. A blank developed in the flat pattern calculator becomes a purchase quantity once you convert its area to pounds. And the same density figures underpin the material-removal side of machining: knowing that steel is 0.2836 lb/in³ turns a chip volume into a chip weight, which is how scrap credit is estimated on high-removal jobs.
One thing weight does not tell you is strength. A heavier section is not automatically stronger — the angle in the worked example carries far more bending load than a round bar of the same weight, because stiffness depends on how far the metal sits from the neutral axis. For the material behaviour itself, the stress and strain calculator covers axial stress and elongation, and the hardness conversion calculator estimates tensile strength when the alloy is unlabelled.
Getting a custom density right when the alloy isn't listed
The eleven listed alloys cover the shapes people search for most, but plenty of real jobs involve something not on the list — a bronze, a nickel alloy, a specific tool steel — and those need the Custom density field instead of a preset. That field expects pounds per cubic inch, and material data sheets rarely report density in that unit, which is where the trouble starts.
Most published densities arrive as kilograms per cubic metre or grams per cubic centimetre. To get from kg/m³ to lb/in³, divide by 27,680 — the same constant that relates carbon steel's 0.2836 lb/in³ to its 7,850 kg/m³ figure elsewhere on this page. A g/cm³ value is numerically the same as a kg/L value, so convert it by multiplying by 1,000 to reach kg/m³ first, or divide it directly by 27.68.
The failure mode that is easy to catch is a decimal slip: typing 7850 where 0.2836 belongs inflates the answer by a factor of 27,680, and the result is obviously wrong on sight. The more dangerous version is entering a g/cm³ figure — commonly a number between 2 and 20 for engineering metals — directly into the lb/in³ field without converting it at all. Because that unconverted number is roughly 27.7 times too large, the weight it produces still looks like a plausible bar or plate weight rather than an obviously broken one, so nothing about the output flags the mistake.
Whenever the material calls for Custom density, work the conversion once on paper — kg/m³ divided by 27,680 — rather than trusting a copied figure to already be in the right unit.