Rebar Weight Calculator
Work out how much reinforcing bar your job needs. Add bars by size, length and count, or sketch a slab and let it lay out the grid for you. You get total weight, total length, bar count, and an order cost - updated live as you type. Everything runs in your browser, nothing uploaded.
Breakdown
Enter bars to see the breakdown
Bar Size Reference
Learn more: estimating rebar weight
Where weight per foot comes from
Rebar weight is set by the bar's cross-section area and the density of steel. For US bars the calculator uses the area (pi/4 times diameter squared) times 12 inches per foot times 0.2836 lb per cubic inch. A #4 bar is 1/2 inch across, so its area is 0.196 square inches and it weighs about 0.668 lb per foot. Metric bars use the nominal mass rule kg/m = 0.00617 times diameter in mm squared, so a 16 mm bar works out to about 1.58 kg/m. These match the standard mill weight tables.
Laying out a slab grid
For a flat slab you place two layers of bar that cross each other. Pick a bar size and a spacing each way, and the count in one direction is the span it crosses divided by the spacing, plus one for the edge bar. Take a 20 ft by 10 ft slab at 12 inch spacing both ways: 11 bars run the long way (each 20 ft) and 21 run the short way (each 10 ft). That is 220 + 210 = 430 linear feet, which at 0.668 lb/ft for #4 bar is about 287 lb before any lap allowance.
Lap splices and ordering by the ton
Bars longer than stock length, or that continue past a joint, overlap and are tied together. The lap-splice allowance adds that overlap as a percentage of total length, so a 10% setting on the 430 ft slab above pushes it to 473 ft. To turn weight into a price, mills sell by the ton (2000 lb) or tonne (1000 kg). Enter your price per ton and the calculator divides total weight by 2000 and multiplies, so 287 lb at $800/ton is about $115.
FAQ
How much does rebar weigh per foot?
Weight per foot depends on bar diameter. A #3 bar (3/8 inch) is about 0.376 lb/ft, a #4 bar (1/2 inch) about 0.668 lb/ft, a #5 (5/8 inch) about 1.043 lb/ft, and a #8 (1 inch) about 2.67 lb/ft. The figure comes from the steel cross-section area times the density of steel (0.2836 lb per cubic inch).
How do I estimate how much rebar a concrete slab needs?
Use the slab grid mode. Enter slab length and width and the bar spacing each way. The number of bars in one direction is the span across it divided by the spacing, plus one for the edge bar. A 20 ft by 10 ft slab with 12 inch spacing both ways needs 11 bars running lengthwise and 21 running crosswise, about 430 linear feet before any lap allowance.
How many feet of rebar are in a ton?
Divide 2000 lb by the weight per foot. For #4 bar that is 2000 / 0.668, roughly 2994 feet per ton. For #5 bar it is about 1918 feet, and for #8 bar about 749 feet. The calculator turns your total weight into a cost using the price per ton or tonne you enter.