Aluminium flat bar weight calculator
Flat bar in aluminium alloy: 12 common sizes with the mass per metre, and a calculator for your own. Aluminium weighs under 35 % of the steel of the same section.
Short answer
The mass per metre of aluminium flat bar is width × thickness × 0.0027 kg (dimensions in millimetres): 40×5 weighs 0.540 kg/m, and a 6 m bar 3.24 kg. For mental arithmetic, every 1000 mm² of cross-section is 2.70 kg/m, so 100×10 weighs 2.70 kg/m and 50×10 and 100×5 weigh 1.35 kg/m each. Aluminium weighs 0.344 of the same section in steel. Mass does not depend on how the bar is laid, but stiffness depends on it a great deal. The common sizes and mass per metre are below.
Common sizes and mass per metre
| Size, mm | Cross-section, mm² | kg/m |
|---|---|---|
| 15×2 | 30 | 0.08 |
| 20×2 | 40 | 0.11 |
| 20×3 | 60 | 0.16 |
| 25×3 | 75 | 0.20 |
| 30×3 | 90 | 0.24 |
| 30×5 | 150 | 0.41 |
| 40×4 | 160 | 0.43 |
| 40×5 | 200 | 0.54 |
| 50×5 | 250 | 0.68 |
| 60×5 | 300 | 0.81 |
| 80×8 | 640 | 1.73 |
| 100×10 | 1 000 | 2.70 |
Where the number comes from
The cross-section works out as F = a · b. For 40×4 mm that is 160 mm², which at a density of 2.70 g/cm³ gives 0.43 kg/m.
Aluminium is welded with TIG on alternating current or with a wire feeder and aluminium wire; the oxide film melts at around 2050 °C, far above the metal itself, and has to come off with a stainless brush immediately before welding. The detail is in welding aluminium.
How to work out flat bar mass by hand
Flat bar is the simplest section there is: F = a · b, width times thickness. The mass per metre is therefore width × thickness × 0.0027 kg (dimensions in millimetres). There are no corners to subtract and no diameters to confuse — errors come mostly from units.
Example: 40×5 flat bar, 6 m length.
- Area: 40 · 5 = 200 mm².
- Mass per metre: 200 × 2.70 / 1000 = 0.540 kg/m.
- A 6 m length: 3.24 kg. Twenty strips of 1.5 m make 30 m, i.e. 16.2 kg.
A reference for mental arithmetic: 1000 mm² of section is 2.70 kg/m. A 100×10 bar has exactly that, 50×10 and 100×5 half, and 30×3 (90 mm²) a bit under a tenth, i.e. 0.243 kg/m.
Flat or on edge: same mass, different stiffness
A flat bar’s mass does not depend on which way you lay it; its stiffness very much does. In bending, the depth in the direction of the load counts to the third power. A 40×5 bar standing on edge (40 mm vertical) is (40/5)² = 64 times stiffer than one lying flat. That is why shelves, brackets and cross bars use flat bar on edge, and flat only where it has to bend or lie against a surface.
Compared with steel of the same size, aluminium weighs 0.344 of the mass but deflects three times as much (modulus 70 000 against 210 000 MPa). On edge, raising the depth about 1.44 times evens out the deflection — and the mass comes to about half the steel. The same calculation for sheet lying flat is in the aluminium sheet calculator.
Flat bar alloys
Extruded flat bar is mostly 6xxx (6060, 6082 — 2.70 g/cm³ each in the site’s density table); strips cut from sheet are 5754, 5083 or 1050A. A 40×5 bar in 5083 (2.66 g/cm³) weighs 0.532 kg/m, in 7075 (2.81 g/cm³) 0.562 kg/m. For an estimate 2.70 is enough; the difference matters when a large batch is settled by the kilogram.
Welding flat bar
- Thick bars. Aluminium conducts heat away much faster than steel, so a 10 mm bar “won’t take” at the start of the weld — the first centimetres often lack fusion. Warming the spot with the arc before adding filler, or starting on a run-on tab, helps.
- Butt-joining strips. Above a few millimetres the edges are bevelled, as with steel; the edge preparation calculator picks the groove.
- Filler. For 6xxx alloys the site’s filler table points to ER 4043 (more resistant to hot cracking), for 5xxx to ER 5356 (stronger, colour-stable after anodising, but not above 65 °C).
- Oxide. A stainless brush right before welding, on the end face too.
Technique details are on the welding aluminium page, and every shape is in the aluminium weight calculator. Round bar has its own page: aluminium round bar.
Common mistakes with flat bar
- Flat bar counted as sheet. Sheet mass is per square metre, flat bar per running metre; 5 mm sheet is 13.50 kg/m², but a 40×5 bar weighs 0.540 kg/m.
- Centimetres instead of millimetres. 4×0.5 instead of 40×5 gives a result a hundred times too small.
- Kerf ignored when cutting strips. A 1250 mm sheet will not give 31 strips of 40 mm — cuts and edge trimming take their share.
- Width and thickness on the order. For mass the order does not matter, for the supplier it does: give width × thickness.
Frequently asked questions
Does the alloy change the weight?
Barely. The density of aluminium alloys runs between 2.66 and 2.80 g/cm³, and trade calculations use 2.70. Across a whole pallet the difference is smaller than the rolling tolerance, so 2.70 is enough for quoting and haulage.
Why does this differ from the weight at the stockist?
Because the dimensional tolerance works both ways, and sheet and section rarely come out at exactly the nominal thickness. On a thin wall the gap reaches a few per cent — order by the tonne with a margin.
Flat bar or a strip cut from sheet — is the mass the same?
Yes, at the same size: 40×3 weighs 0.324 kg/m whether it is extruded or cut from 3 mm sheet (8.10 kg/m² × 0.04 m). They differ in tolerance and edge, not in the formula. When cutting strips from a sheet, remember that every cut eats some of the width.
How much does a 100×10 aluminium flat bar weigh?
2.70 kg/m: a 1000 mm² section times 2.70 g/cm³. That is a handy reference point — every 1000 mm² of aluminium section is 2.70 kg per metre, so a 50×10 bar weighs half of that, and so does a 100×5.
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