IronBid rebar calculator
One system to calculate your bar list weight, the rebar in a slab or mat, and convert bar diameters between millimeters and inches — using US bar sizes #3 through #11.
How to calculate rebar weight from a bar list
Multiply each bar size's weight per foot by the length and quantity, add up every line and apply a waste factor for laps and cut-offs (typically 3% to 8%). The calculator returns the total in pounds and short tons, ready to price.
Slab and mat rebar
For a two-way mat, the number of bars in each direction equals the perpendicular dimension divided by the spacing, plus one. The result includes the steel ratio in lb/ft² so you can compare bar size and spacing options before you bid.
Rebar sizes in inches and millimeters
US bar numbers indicate the nominal diameter in eighths of an inch: a #4 bar is 4/8" = 1/2" (12.7 mm). Use the converter and the equivalence chart when you work with metric drawings or imported steel.
Frequently asked questions
How much does a #4 rebar weigh?
A #4 bar (1/2", 12.7 mm) weighs 0.668 lb per foot. A standard 20 ft stick weighs about 13.4 lb.
What is #5 rebar in millimeters?
A #5 bar has a nominal diameter of 5/8", which equals 15.9 mm. Its closest metric equivalent is a 16 mm bar.
What waste factor should I use for rebar?
Most rebar estimators use 3% to 8% depending on lap splices, stock lengths and project complexity. Use the higher end for jobs with many hooks, bends and short pieces.