Rebar Weight Calculator
Rebar mass from diameter and length, both directions: kilograms for a cutting list, or metres inside a bought tonne. Standard diameters use the exact GOST 5781 table; anything else falls back to the estimator's d²/162 — and the page shows metres per tonne and whole 12-metre bars to buy.
The estimator's oldest constant
Every reinforcement estimate on every site runs through one number: 162. It compresses steel's density and a circle's area into a division you can do at the yard — 12 mm bar is 144/162, near 0.89 kg per metre; a tonne of it is about 1126 metres.
The two directions of this page are the two moments of a build: the cutting list (length known, tonnage wanted, for the order) and the delivery check (mass known, metres wanted, to see whether the truck matches the invoice).
Frequently asked questions
Where does d²/162 come from?
From steel's density. A round bar's mass per metre is π/4 × d² × 7850 kg/m³, and collapsing the constants gives d²/162.2 — rounded to 162 in every estimator's head. It is not a convention but a consequence: only the density is assumed.
Why does the table differ from the formula slightly?
Because ribbed rebar is not a perfect cylinder — the ribs add metal the formula's ideal circle does not see. GOST 5781 publishes measured nominal masses per diameter; they sit within about half a percent of d²/162, and this page prefers the table wherever one exists.
How much does a typical slab actually need?
A 10-centimetre slab with a 200 mm mesh of 12 mm bar uses about 10 metres of bar per square metre — roughly 8.9 kg/m². Twenty square metres is then ~178 kg. The point of the metres-per-tonne line is exactly this arithmetic in reverse at the yard.
Why count 12-metre bars?
Because that is the length mills ship and yards sell; shorter stock is cut from it. Dividing your total length by 12 and rounding up tells you what actually goes on the truck — and the leftover from the rounding is your lap-splice and cutting allowance.
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