Steel Weight Formula for Rebar: The Complete Guide (with Free Excel Calculator)

 

If you work in construction, structural design, or estimating, you already know that getting the steel weight right can make or break a bill of quantities. Order too little rebar and you stall the pour; order too much and you're eating the cost of wasted steel. The good news is that the entire calculation comes down to one simple formula.

The Steel Weight Formula

The standard formula used across the construction industry (based on IS 1786) is:

Weight (kg) = D² × L / 162

Where:

• D = Bar diameter (mm)
• L = Length of the bar (m)
• 162 = A constant derived from the density of steel (7850 kg/m³) and the cross-sectional area of a round bar

This formula works because it converts the bar's volume into weight using steel's known density, simplified into a single constant so you don't have to calculate cross-sectional area every time.

Example

For a 12mm bar that is 1 meter long:

Weight = (12² × 1) / 162 = 0.089 kg/m (rounded to 0.888 kg per full meter of a single bar length used in tables — see reference table below)

Bonus Formula: Length of Steel in 1 Ton

Estimators often need the reverse calculation — how many meters of a given bar diameter make up 1 ton (1000 kg) of steel. Flip the weight formula around and you get:

Length (m) = 1000 × 162 / D²  =  162000 / D²

This is especially useful when you're pricing steel by length but purchasing by weight (or vice versa).

Quick Reference Table: Length in 1 Ton of Steel

Bar Diameter (mm)	Length in 1 Ton (m)
8	2531
10	1620
12	1125
16	633
20	405
25	259
32	158

Memory Tip

• • Weight (kg) = D² × L ÷ 162
• • Length (m) for 1 Ton = 162000 ÷ D²

Keep these two lines handy — they cover almost every rebar weight question you'll face on site or at the desk.

Doing this math by hand for every bar in a bar bending schedule gets tedious fast.

Download the free, ready-to-use Steel Weight Formula Calculator in Excel — just enter the diameter and length, and it does the rest.

Download the Excel Steel Weight Calculator

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Have a project where you need a full Bar Bending Schedule (BBS) with multiple bars, cutting lengths, and totals? Check out the related Rebar Weight Calculator for a complete BBS-style spreadsheet.