Nobody weighs one bar
Every other metal weight calculator gives you one section at a time. That is not the question. The question is what the whole lot weighs: for the van, for the lift, for the delivery note.
So this is a cutting list. Add the posts, the rail, the base plates and the infill bar, in different shapes and different materials, and get a total with each line shown against it.
Three things other calculators get wrong
1. Hexagon bar
Across the flats, the area is 0.866 × AF²: precisely (√3/2) times the square of the size across flats. Not the size squared, which is the square that contains it. Not π r², which is the circle inside it.
It is the shape people most often fudge, and measuring across the corners instead of the flats gives a third answer again.
2. Hollow sections have rounded corners
Calculate a box section as a sharp-cornered rectangle minus a sharp-cornered rectangle and you get a figure that is too heavy. A real RHS or SHS is radiused inside and out, so there is material missing at all four corners.
On a thin wall it barely registers. On a small section with a thick wall it is a few per cent, which is enough that your number and the mill certificate disagree and nobody can work out why. The tool applies the four-corner deduction and tells you on the row that it has.
3. Stainless is not mild steel
304 and 316 are around 8,000 kg/m³ against 7,850 for carbon steel: about two per cent heavier.
On one handrail nobody cares. On a tonne order it is twenty kilos. And on a lift running near the rated capacity, or a van already close to its plate, two per cent is exactly the sort of margin that decides it.
Galvanising is not free weight
Hot dip galvanising adds roughly three to five per cent, and the tool adds four as a working figure for structural sections.
The important part is that it is not proportional to weight, it is proportional to surface area. A pallet of thin balustrade posts gains a much bigger percentage than a beam does, because there is far more surface per kilo. Anybody who has had a galvanised order come back heavier than expected has met this.
An impossible section returns nothing
Type a 20mm tube with a 10mm wall and this tool gives you nothing, and says the section cannot exist.
Most calculators will happily return a negative weight there, or a nonsense positive one, because the arithmetic does not care. A wall thicker than half the outside diameter is not a very thick tube; it is a typo. Rows like that are left out of the total rather than quietly subtracted from it.
For a rolled section, use the catalogue
There is a shape in the list called "from a catalogue kg/m" and for a UB, UC, PFC or any other rolled section it is the right one to use.
A rolled section has root radii, toe radii and on older sections tapered flanges. No simple formula reproduces that, and the published mass per metre is measured rather than derived. Anything that claims to calculate a universal beam from three dimensions is approximating something already published exactly.
How accurate is any of this?
Accurate enough that rolling tolerance matters more than anything in the assumptions. Real material comes with a thickness tolerance, and on thin sheet in particular that moves the weight by more than the corner radii or the density figure ever will.
Which is the honest answer: use this to order, to load and to price. If you need a weight to the kilogram for a certificate, weigh it.
Next to it: what the grade suffixes mean, and whether the van will take it.
Common questions
How do I work out the weight of a steel section?
Cross-sectional area in square millimetres, divided by a million to get square metres, times the length in metres, times 7,850 kg per cubic metre for steel. A 100 × 10 flat is 1,000 mm², which is 7.85 kg per metre. The tool does all of it and shows the area and the kg/m so you can check the working.
How do you calculate the area of hexagon bar?
Across the flats, the area is 0.866 times the square of the size: (√3/2) × AF². Not the size squared, and not π r². It is the shape most often fudged, and measuring across the corners instead of the flats gives a different number again.
Why is my box section lighter than my calculation?
Because a real hollow section has radiused corners, inside and out. A sharp-cornered sum over-estimates it, and on a small section with a thick wall the error is a few per cent: enough that it will not match the mill certificate. This tool applies the four-corner deduction and says it has.
Is stainless heavier than mild steel?
Yes, by about two per cent. 304 and 316 come in around 8,000 kg/m³ against 7,850 for carbon steel. On one handrail nobody notices. On a tonne it is twenty kilos, and on a lift running near the rated capacity that is the kind of margin that matters.
How much does galvanising add?
Roughly three to five per cent on a typical structural coating, and the tool adds four. It depends on the surface-area-to-mass ratio of the section, so thin work gains proportionally more than heavy work. Balustrade posts gain more than a beam does.
What about a UB or a UC?
Use the published kg per metre from the catalogue: there is a shape in the list for exactly that. A rolled section has root radii and tapered flanges that no simple formula reproduces, and the published figure is the most accurate route there is.