Rebar Weight Calculator — Steel kg/m

Steel is bought by weight but drawn on a bar bending schedule by size, length and count, so somebody has to convert one into the other before the order goes out. This Rebar Weight Calculator takes the schedule row by row, totals it per bar size, adds a wastage allowance for laps and offcuts, and prices it if you give a rate. It works in millimetre bars and kilograms, or in US bar sizes, feet and pounds.

Worked Example: A Small Footing and Column Order

The tool opens on three rows: 40 bars of 12 mm and 60 bars of 10 mm, all 12 m long, plus 150 links of 8 mm cut at 1.2 m.

• 12 mm: 0.8878 kg/m × 480 m = 426.15 kg
• 10 mm: 0.6165 kg/m × 720 m = 443.91 kg
• 8 mm: 0.3946 kg/m × 180 m = 71.03 kg
• 941.08 kg net, and 988.14 kg (0.988 tonnes) once 5% wastage is added

Rows with the same bar size are merged in the summary table, so a schedule that lists 12 mm bars in five places still gives one line to order from. Load Sample also cycles through a priced slab mesh, a US order in #5 and #4 bars, and a beam with 16 mm and 20 mm mains.

How the Math Turns D²/162 into Kilograms

A round bar of diameter d has a cross-section of πd²/4. Multiply by the density of steel, 7,850 kg/m³, and convert millimetres to metres, and the weight of one metre comes out as d² ÷ 162.2. That is the site rule “D²/162” with the divisor rounded, and the tool keeps the unrounded figure, so a 16 mm bar is 1.5783 kg/m rather than 1.5802. Over a 2-tonne order the difference is about 2.4 kg.

US bars do not use the formula. Their weights come straight from ASTM A615, the table mills and estimators quote: #4 is 0.668 lb/ft and #8 is 2.670 lb/ft. A collapsed reference table under the results lists every size with the weight of one 12 m bar, or one 20 ft bar for US sizes.

Limits of the Weight Figure

The weight assumes plain round bars at nominal size. Ribbed TMT bars are rolled to the same nominal weight, but each standard allows a rolling tolerance of a few percent either way, so the weighbridge will not match to the kilogram. Wastage is capped at 50%; a figure above that stops with “Wastage must be between 0 and 50 percent.” The count must be whole, so 2.5 bars is refused with “Row 1: number of bars must be a whole number of 1 or more.”

Lap lengths, hooks and bends are not added for you. Either include them in the cut length of each row or cover them with the wastage percentage, which is why 5% is the starting value.