Weight per foot, per bar and per order — and the difference between them
← Back to the calculatorWeight = length × weight per foot. #4 is 0.668 lb/ft and #6 is 1.502 lb/ft. In metric, kg/m = d² ÷ 162.2, so a 16 mm bar is 1.578 kg/m.
But the weight that pays the invoice is not the steel in the slab — it is the steel you order, which also carries the laps and the offcut. Both are split out below.
Everything on this page comes out of these. The first two are exact; the third is the one you can do in your head.
The third line is the useful one: 4² ÷ 24 = 0.67 lb/ft. It works for any bar number up to about #8, and it is why doubling the bar number roughly quadruples the weight.
The five sizes that cover most residential and light commercial work. The complete chart — every imperial size from #3 to #18 and metric 10 mm to 40 mm, with areas and bars per ton — is on the rebar size and weight chart.
| Bar | lb / ft | 20 ft bar (lb) | 40 ft bar (lb) | lb per 100 ft |
|---|---|---|---|---|
| #3 | 0.376 | 7.5 | 15.0 | 37.6 |
| #4 | 0.668 | 13.4 | 26.7 | 66.8 |
| #5 | 1.043 | 20.9 | 41.7 | 104.3 |
| #6 | 1.502 | 30.0 | 60.1 | 150.2 |
| #8 | 2.670 | 53.4 | 106.8 | 267.0 |
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| Size | kg / m | 12 m bar (kg) | kg per 100 m |
|---|---|---|---|
| 10 mm | 0.617 | 7.4 | 61.7 |
| 12 mm | 0.888 | 10.7 | 88.8 |
| 16 mm | 1.578 | 18.9 | 157.8 |
| 20 mm | 2.466 | 29.6 | 246.6 |
| 25 mm | 3.853 | 46.2 | 385.3 |
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For a square grid, a one-foot square of slab holds one foot of bar in each direction — two feet of bar in total. So the weight per square foot is just 2 ÷ spacing × weight per foot, and at 24 in spacing it is the weight per foot itself.
| Bar | lb / ft | 12 in | 16 in | 18 in | 24 in |
|---|---|---|---|---|---|
| #3 | 0.376 | 0.752 | 0.564 | 0.501 | 0.376 |
| #4 | 0.668 | 1.336 | 1.002 | 0.891 | 0.668 |
| #5 | 1.043 | 2.086 | 1.564 | 1.391 | 1.043 |
| #6 | 1.502 | 3.004 | 2.253 | 2.003 | 1.502 |
| #8 | 2.670 | 5.340 | 4.005 | 3.560 | 2.670 |
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Read it as pounds of rebar per square foot of slab. A #4 grid at 12 in on centre is 1.336 lb/sq ft; the same #4 at 18 in drops to 0.891 lb/sq ft.
A 24 ft × 20 ft slab, #4 bar at 12 in on centre, 3 in edge clearance, 20 ft stock bars. The takeoff gives 938 ft of steel in the slab and 49 bars to order. Here is what each part weighs.
| Part | Length | Working | Weight |
|---|---|---|---|
| Steel in the slab | 938 ft | 938 × 0.668 | 626.6 lb |
| Laps (20 laps × 20 in) | 33.3 ft | 33.33 × 0.668 | 22.3 lb |
| Offcut (49 bars = 980 ft) | 8.7 ft | 8.67 × 0.668 | 5.8 lb |
| Order weight | 980 ft | 980 × 0.668 | 654.6 lb |
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The three parts add to 654.7 lb because each was rounded to 0.1 lb; the exact figure is 654.6 lb. You pay for 654.6 lb and you install 626.6 lb. The 28 lb difference is laps and offcut — 4.3% of the order, and it is real money at any price per pound.
All the figures on this site are nominal: calculated from the bar designation and the density of steel, not measured from a physical bar. Coated bar — epoxy or galvanised — weighs more than the nominal figure for the same size, and rolled bars are allowed to vary from nominal within the mill tolerance printed on the certificate.
Yards quote either per bar or per pound, and the two are not interchangeable — a per-bar price already carries the offcut, a per-pound price does not. Convert with one multiplication:
Take the 654.6 lb order above. At a quoted $0.85 per pound it is $556; at $1.10 per pound it is $720. Substitute your own quote — the point is that a 4.3% weight difference between two takeoffs is a 4.3% difference in the bill, so it is worth getting the laps right before you order rather than after.
The metric rule is shorter than the imperial one and just as easy to do in your head: kg/m = d² ÷ 162.2, with d in millimetres.
A standard 12 m bar is the length that matters in metric markets, so 16 mm bar is 18.9 kg per stick and about 52 sticks to the tonne. The full metric table, including areas and bars per tonne, is on the size and weight chart.
#4 is the size most people search for by name, so here it is on its own:
| Measure | #4 (0.500 in / 12.7 mm) |
|---|---|
| Per foot | 0.668 lb |
| Per 20 ft stick | 13.4 lb |
| Per 40 ft stick | 26.7 lb |
| Per 100 ft | 66.8 lb |
| Per metre | 0.994 kg |
| 40 ft bars per ton | about 74 |
| Feet per ton | about 2,994 ft |
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Two independent routes agree here, which is a good way to check any rebar weight: 0.668 lb/ft × 1.4882 = 0.994 kg/m, and 12.7² ÷ 162.2 = 0.994 kg/m. Same bar, two formulas, 0.03% apart.
#4 weighs 0.668 lb per foot, #5 is 1.043, #6 is 1.502 and #8 is 2.670. For any imperial size #3 to #8 the quick estimate is the bar number squared divided by 24, so 4² = 16, divided by 24 gives 0.67 lb per foot. In metric, kilograms per metre = diameter² ÷ 162.2, so a 16 mm bar is 1.578 kg/m.
A #4 bar weighs 0.668 lb per foot. That is 13.4 lb for a 20 ft stick and 26.7 lb for a 40 ft stick, and roughly 74 forty-foot bars to a ton. The metric equivalent, 12.7 mm, comes out at 0.994 kg/m, so the two systems agree to within 0.05%.
Because you buy whole bars. The steel in the slab is the net length, and on top of that you carry the laps where bars join and the offcut left at the end of each line. On a 24 ft × 20 ft slab with 20 ft bars, 626.6 lb of steel in the slab becomes a 654.6 lb order: 22.3 lb of laps and 5.8 lb of offcut.
One pound per foot is 1.4882 kilograms per metre, so 0.668 lb/ft is 0.994 kg/m. Going the other way, one kilogram per metre is 0.6720 pounds per foot. For the same nominal bar the two systems agree to within 0.05%.