Rebar Calculator

Your details

The longer side of the slab. Bars running the other way are spaced along this length.
ft
ft
Center-to-center distance between parallel bars. 12 in (30 cm) is a common slab grid.
in
How far the outer bars sit in from each slab edge. 3 in (7.5 cm) is typical for slabs on grade.
in
#4 (13 mm) is the usual choice for residential slabs on grade.
Extra steel for lap splices where bars join and for cut offcuts. 10% is a common allowance.
%
Used to work out how many full stock bars to buy.
Currency
Total rebar length (with waste)
510.4 ft
Bars running lengthwise12
Bars running widthwise20
Bars in the grid32
Net length (no allowance)464 ft
Lengthwise steel234
Widthwise steel230
Total weight (with waste)341 lb
Stock bars to buy26

You need about 32 bars, 510.4 ft of #4 rebar weighing 341 lb.

  • Bars each way is the grid dimension divided by the spacing, rounded down, plus one to close the edge of the grid.
  • The grid is pulled in from the slab edges by your clearance, so each bar is shorter than the full slab side.
  • Total length already includes 10% for lap splices and offcuts; the weight uses the ASTM #4 bar mass.

Next stepBuy 26 stock bars and round up to whole feet; confirm the bar size, spacing and lap lengths against your slab drawings.

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