The weight per metre is not the hard part
Every site knows 12mm is 0.888 a metre. What takes an hour is turning a drawing into a schedule somebody can price and cut from: bar mark, where it goes, size, cut length, number, shape, weight, and totalled by size, because that is how rebar is bought and how it arrives.
So that is what this produces. The arithmetic is the easy bit and it is done properly: 0.006165 × d², which is just the area of the bar times the density of steel. Calculated rather than looked up, so a 14mm bar or anything else off the standard list still comes out right.
Two things that catch people
Bars come in 12 metre stock lengths
Order 20 bars at 3 metres and, unless somebody thinks about it, that is 20 stock bars with 9 metres thrown off each. 180 metres of steel in the skip.
The tool shows that number, what nesting nothing would cost, because it is the number that makes the case for doing it properly. Four 3-metre bars come out of one 12-metre stock length, and the cutting list tool does the nesting including the cut itself. It was written for timber and the arithmetic is identical.
Weight is what gets delivered and lifted
Rebar is bought by the tonne. A modest reinforced slab is comfortably over one, and a tonne of steel arrives on a wagon, in bundles, not in the back of a van.
It needs somewhere to go that is not the neighbour's drive, and something to move it that is not three lads and a wheelbarrow. The tool says so once the total passes a tonne, which is early enough to do something about it.
Bar marks are not optional
A schedule without marks cannot be checked against the drawing. And on site, steel without marks arrives as an anonymous pile of very similar-looking bars: a 12 and a 16 are hard to tell apart at ten feet, and a 5.8m and a 5.9m are impossible.
The tool nags about unmarked rows for exactly that reason.
What it will not do, and why
It will not give you a lap length. That is a design output: it depends on bond conditions, concrete strength, cover, bar size and the stress in the bar. It is not a rule of thumb and it is not ours to publish.
This site removed twelve structural tools for exactly that reason: a note under a number does not change what the number does when somebody builds from it. So the tool flags any bar longer than a stock length, tells you a lap is coming, and points at the drawing.
It also does not decide what reinforcement anything needs, what size the bars should be, or where they go. It schedules bars you have taken off a drawing somebody else signed.
Shape codes are recorded, not checked. They go through exactly as typed and are not validated against BS 8666, because a schedule that quietly corrected a shape code would be more dangerous than one that left it alone.
Next to it: concrete volumes, which mix to order: the RC designations are the ones for concrete with steel in it, and metal weights for everything that is not rebar.
Common questions
How much does rebar weigh per metre?
It is 0.006165 times the diameter squared, in kilograms per metre, which is just the area of the bar times the density of steel. A 12mm bar is 0.888 kg/m, 16mm is 1.579, 20mm is 2.466, 25mm is 3.854. This tool calculates rather than looks them up, so an unusual size still comes out right.
What is a bar schedule?
The list a merchant prices and cuts from: bar mark, where it goes, size, cut length, number, shape code and weight, totalled by size. The weight per metre is trivial and every site knows it. Turning a drawing into a sendable schedule is the hour of work, and that is what this is for.
How long does rebar come in?
Generally 12 metre stock lengths, cut to your schedule. Which matters more than it sounds: order 20 bars at 3 metres and you are notionally buying 20 stock bars and throwing 9 metres off each, unless the cuts get nested properly.
Will it work out my lap lengths?
No, deliberately. Lap length is a design output: it depends on bond conditions, concrete strength, cover, bar size and the stress in the bar. It comes off the drawing or from whoever designed the reinforcement. This tool flags bars longer than a stock length so you know a lap is coming, and then stops.
Does it check my shape codes?
No. Shape codes are recorded exactly as you type them and are not interpreted or validated against BS 8666. A schedule that quietly corrected a shape code would be worse than one that did not touch it.
Why does it warn me about the weight?
Because rebar is bought by the tonne and it arrives in bundles that have to be moved. A modest reinforced slab is well over a tonne of steel, and it turns up on a wagon rather than in a van. Knowing that before the delivery is booked is worth the two seconds.