What formula gives rebar weight?

Weight per length comes from the steel density and cross-sectional area. For US bars, weight = 0.00249 x d squared lb/ft where d is the bar number (eighths of an inch). For metric, weight = 0.00617 x d squared kg/m where d is the diameter in millimetres.

What does a bar number mean?

A US rebar number is the nominal diameter in eighths of an inch. A #4 bar is 4/8 inch, that is 1/2 inch in diameter. A #8 bar is 8/8 inch, one inch. The number squared drives the weight per foot.

How accurate is the calculated weight?

The formula matches the published nominal weights in ASTM A615 and standard metric tables to within rounding. Real coils vary slightly with mill tolerance and deformation pattern, so add a small allowance when ordering by weight.

How do I convert to tonnes for ordering?

Divide the total kilograms by 1000 for metric tonnes, or divide pounds by 2000 for US short tons. Suppliers usually price reinforcing steel by the tonne, so the total weight here converts directly to a quantity to order.

Does this include tie wire or laps?

No. It is the bar steel only. Add roughly 2 to 5 percent for lap splices and a small allowance for tie wire and waste when estimating a full reinforcement package.

Rebar Weight Calculator

Reinforcing steel is bought and lifted by weight, so estimating tonnage accurately matters for both cost and crane planning. This calculator uses the exact density-based formulas behind the published bar weight tables to give the weight of any number of identical bars in both pounds and kilograms.

How it works

Weight per unit length is proportional to the square of the bar diameter:

imperial: w = 0.00249 × d²  lb/ft   (d = bar number, eighths of an inch)
metric:   w = 0.00617 × d²  kg/m     (d = diameter in mm)
total = w × number of bars × length per bar

A #5 bar is 5/8 inch, so 0.00249 x 25 = 1.043 lb/ft, matching the table value. A 16 mm bar gives 0.00617 x 256 = 1.58 kg/m. The total simply multiplies by the count and length.

Example and notes

Forty #6 bars, each 20 ft long: 0.00249 x 36 = 0.896 lb/ft, x 20 x 40 = about 717 lb (325 kg). Add 2 to 5 percent for lap splices and a little for tie wire and cutting waste when placing a real order. The figures here are bar steel only and match ASTM A615 nominal weights to within rounding.