Rebar calculator
A mat is two sets of bars at right angles. Count them, add laps, and weigh the result.
%
Total bar length
246.75m
- Total weight
- 219.1
- Bars running lengthwise
- 20
- Bars running crosswise
- 30
- Total bars
- 50
- Mass per metre of bar
- 0.888 kg/m
- Rough steel area ratio
- 0.0236 %
Show the working
- Slab length = 6
- Slab width = 4
- Bar spacing = 200
- Bar diameter = 12
- Edge cover = 50
- Lap allowance = 5
- Bars running lengthwise = floor((4 - 2*50/1000) / (200/1000)) + 1 = 20
- Bars running crosswise = floor((6 - 2*50/1000) / (200/1000)) + 1 = 30
- len_long = 20 * (6 - 2*50/1000) = 118
- len_short = 30 * (4 - 2*50/1000) = 117
- Total bar length = (118 + 117) * (1 + 5/100) = 246.75
- Mass per metre of bar = pi * (12/2000)^2 * 7850 = 0.887 814
- Total weight = 246.75 * 0.887 814 = 219.068
- Total bars = 20 + 30 = 50
- Rough steel area ratio = 6*4 > 0 ? 50 * pi * (12/2000)^2 / (6*4) * 100 : 0 = 0.023 561 9
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- bars = floor(clear span / spacing) + 1
- mass per metre = pi (d/2)^2 x 7850 kg/m3
A 12 mm bar weighs 0.888 kg/m, a 16 mm bar 1.58 kg/m — both derived here rather than looked up.
Reinforcement design is a structural matter. This counts bars; it does not tell you what size or spacing you need.