Khanal Group

Concrete & steel quantity estimator

Concrete volume for slabs, beams, columns and footings, the cement bags, sand and aggregate for a nominal mix, and the weight of reinforcement by bar diameter. These are estimating rules of thumb for ordering and checking BOQ quantities, not a mix design.

Rules as on 22 October 2026
One member type per line. For a column use its height as the depth.
Cement : sand : coarse aggregate by volume
Dry materials needed per m³ of wet concrete; 1.52 to 1.57 is also used
50 kg ÷ 1,440 kg/m³ bulk density
Total length = number of bars × cutting length, including laps and hooks.

The rules used

  • Concrete volume = length × breadth × depth × number, in cubic metres, added across members. Deduct openings yourself; nothing is deducted for steel.
  • Dry volume = wet volume × 1.54. Loose cement, sand and aggregate shrink when water is added and voids fill, so about 54% more dry material is needed. The factor is an input.
  • Materials: for a mix 1 : s : a, cement volume = dry volume ÷ (1 + s + a); sand = cement volume × s; aggregate = cement volume × a. Cement bags = cement volume ÷ 0.0347 m³, the volume of a 50 kg bag at 1,440 kg/m³.
  • Steel weight per metre = D² ÷ 162 kg, with D in mm. It comes from the density of steel, 7,850 kg/m³: π/4 × D² × 7,850 ÷ 10⁶ = D² ÷ 162.2. An 8 mm bar weighs 0.395 kg/m, 12 mm 0.889 kg/m, 16 mm 1.58 kg/m.

Worked example

One slab 6 × 4 × 0.15 m (3.6 m³), four beams 4 × 0.23 × 0.45 m (1.656 m³), six columns 0.3 × 0.3 × 3 m (1.62 m³) and six footings 1.5 × 1.5 × 0.45 m (6.075 m³) total 12.951 m³ of concrete. In M20 (1 : 1.5 : 3), dry volume is 12.951 × 1.54 = 19.945 m³; cement = 19.945 ÷ 5.5 = 3.626 m³, or 104.5 bags (order 105); sand 5.44 m³; aggregate 10.88 m³. Steel: 600 m of 8 mm (237.04 kg), 450 m of 12 mm (400.00 kg) and 240 m of 16 mm (379.26 kg) weigh 1,016.3 kg.

What these numbers are not

Nominal mix ratios are a site convention for small and non-structural work. IS 456:2000 prefers design mix concrete and permits nominal mix only for M20 or lower (check); M25 and above should come from a design mix to IS 10262, whose cement content depends on the materials, workability and exposure. The 1:1:2 ratio for M25 is shown because sites still use it for estimating, not because the code allows it. Sand bulking, moisture and wastage change real consumption; use your mix design and BOQ specification for billing.

Sources: IS 456:2000 Plain and Reinforced Concrete, Code of Practice (Bureau of Indian Standards) on nominal and design mix; IS 10262 for mix design; steel weight derived from 7,850 kg/m³. Checked 22 October 2026.

Common questions

How many cement bags are there in 1 m³ of M20?

By this rule, 1.54 ÷ 5.5 ÷ 0.0347 = about 8.07 bags of 50 kg for 1 m³ of 1:1.5:3 concrete, before wastage. A design mix for M20 can need more or less cement.

Why multiply by 1.54?

The wet volume of concrete is smaller than the loose volume of the dry materials, because sand fills the voids in aggregate and cement fills the voids in sand. 1.54 is the factor most estimators use; some use 1.52 or 1.57.

Does D²/162 include laps and wastage?

No. It gives the weight of a straight bar of the length you enter. Put laps, hooks and bends into the cutting length, and add rolling margin or wastage as your estimate requires.

Can I use M25 as a nominal mix?

IS 456:2000 allows nominal mix only up to M20 (check). For M25 and above, use a design mix; the 1:1:2 ratio here is only an estimating guide.