How many cement bags are in 1 cube of concrete?

A cube is 100 ft³ ≈ 2.83 m³ of finished concrete. At a 1:2:4 nominal mix that works out to about 18 bags of 50 kg cement (6.34 bags/m³ × 2.83). A richer 1:1.5:3 mix needs about 22.8 bags per cube. Sand and metal for a 1:2:4 cube come to roughly 0.44 and 0.88 cube respectively.

What is the mix ratio for a house slab in Sri Lanka?

Most domestic ground and roof slabs use 1:2:4 (Grade 15) for plain sections, or 1:1.5:3 (Grade 20) where the slab is reinforced and carries load. Columns and heavily loaded members often step up to 1:1:2 (Grade 25). Always follow your engineer's drawing for reinforced structural work.

How much sand and metal do I need for 1 cubic metre of concrete?

For 1 m³ of 1:2:4 concrete you need about 6.34 bags of cement, 0.44 m³ (15.5 ft³) of sand and 0.88 m³ (31 ft³) of metal — the extra volume comes from the ×1.54 dry-volume factor. That is roughly 0.15 cube of sand and 0.31 cube of metal per cubic metre.

What does 1:2:4 mean in concrete?

It is the ratio of cement to sand to coarse aggregate (metal) by loose volume — 1 part cement, 2 parts sand, 4 parts metal. A lower middle-and-last number means more cement per batch and a higher-strength, higher-grade concrete. 1:2:4 is the common general-purpose nominal mix in Sri Lanka.

How many bags of cement for a 20 × 15 slab?

For a 20 ft × 15 ft slab poured 5 inches thick at 1:2:4 with 5% wastage, you need about 24 bags of cement, 0.58 cube of sand, 1.16 cube of metal and roughly 589 litres of water. Change the thickness or mix in the calculator and every figure updates instantly.

Why does the calculator multiply by 1.54?

Dry cement, sand and metal have air voids that fill in once mixed with water, so a batch shrinks by about 35% from dry to wet. To get enough dry material for a given wet volume you scale up by 1/(1−0.35) ≈ 1.54. This dry-volume factor is the standard concrete-estimation convention used in CIDA and IS 456 rate build-ups.

Does this include reinforcement steel?

No. This calculator covers only cement, sand, metal and water for the concrete itself. For rebar quantities and weights use the Sri Lanka steel bar weight calculator. Formwork, labour and ready-mix delivery are also outside its scope.

Can I use it for designed high-grade mixes like M30?

No. It covers nominal mixes up to about M25 (1:1:2), which are proportioned by fixed volume ratios. Grade M30 and above need a proper IS 10262 mix design using the tested properties of your specific aggregates, so a fixed ratio would be unsafe. Use it for domestic and light structural work only.

Sri Lanka · Construction

Sri Lanka Concrete Mix Calculator

Find exactly how many cement bags, cubes of sand and metal, and litres of water your pour needs. Enter a slab, footing, column or beam, pick a nominal mix like 1:2:4, and get a hardware-ready material list — in the cubes and cubic feet masons order in. Free, no signup, sources cited.

By Induwara Ashinsana— Executive Director, Ryzera TechnologiesUpdated Jul 11, 2026

Concrete material estimatenominal mix

Dry-volume method · ×1.54

Length

Width

Thickness

Mix ratio (cement : sand : metal)

Grade 15 (M15) — General house slabs, floors, non-structural work

Wastage allowance (%)

Extra to order for spillage and over-excavation. 5% is typical.

Cement

24bags (50 kg)

1,177 kg total

Sand

0.58cube

57.8 ft³ · 1.64 m³

Metal (aggregate)

1.16cube

115.5 ft³ · 3.27 m³

Water

589litres

at chosen water-cement ratio

Reference

Wet volume

3.54 m³

125 ft³

Dry volume (×1.54)

5.72 m³

after wastage

Grade / cross-check

Grade 15 (M15)

6.65 bags/m³

Material split (dry volume)

Cement: 0.82 m³Sand: 1.64 m³Metal: 3.27 m³

Sources: CIDA Method of Measurement (SL site units), SLS 107 (50 kg bag, cement density 1440 kg/m³) and IS 456:2000 Table 9 (nominal mixes). 1 cube = 100 ft³. Estimates for ordering only — confirm with your engineer for structural work.

How it works

The calculator uses the nominal-mix dry-volume (absolute-volume) method — the same estimating convention used in CIDA/ICTAD rate build-ups and the IS 456:2000 nominal mixes widely followed on Sri Lankan sites. It converts your pour into a dry quantity of each material, then reports cement in 50 kg bags and sand and metal in the volumetric units hardware stores sell in.

Wet volume. From dimensions, all measurements are converted to metres and multiplied (V = L × W × T). By volume, cubes (×2.832 m³), cubic feet (÷35.3147) or m³ are used directly.
Wastage. The wet volume is scaled by (1 + wastage/100) so you order enough for spillage and over-excavation.
Dry volume. Multiply by 1.54. Loose dry materials lose about 35% of their bulk once mixed with water, so 1/(1−0.35) ≈ 1.54 gives the dry quantity needed for that wet volume.
Ratio split. For a mix a:b:c with sum S = a+b+c, the dry volume is split cement = D×a/S, sand = D×b/S, metal = D×c/S.
Cement mass & bags. Cement volume × 1440 kg/m³ (SLS bulk density) gives the mass; dividing by 50 kg (SLS 107 bag) and rounding up gives whole bags.
Sand & metal. Sold by volume in Sri Lanka, so each is shown in m³, then ft³ (×35.3147), then cubes (÷100 ft³).
Water. Litres = water-cement ratio × cement mass in kg (1 litre of water ≈ 1 kg).

As a credibility cross-check, the per-cubic-metre cement figure the tool reports reproduces the published nominal-mix values exactly: 1:2:4 → 6.34 bags/m³ and 1:1.5:3 → 8.06 bags/m³. If your figure lands within rounding of these, the estimate is sound. Nominal mixes cover work up to about Grade 25 — designed high-grade concrete (M30+) needs an IS 10262 mix design and is out of scope here.

Worked examples

House slab — 1:2:4

20 ft × 15 ft × 5 in, 5% wastage

Wet V = 6.096 × 4.572 × 0.127 = 3.540 m³ (= 125 ft³)
After 5% wastage: 3.540 × 1.05 = 3.717 m³
Dry D = 3.717 × 1.54 = 5.724 m³; ratio sum = 7
Cement = 5.724 ÷ 7 = 0.818 m³ → 1177 kg → 23.55 → 24 bags
Sand = 5.724 × 2/7 = 1.635 m³ = 57.8 ft³ = 0.58 cube
Metal = 5.724 × 4/7 = 3.271 m³ = 115.5 ft³ = 1.16 cube
Water @ 0.50 = 0.50 × 1177 = 589 litres

1 m³ footing — 1:1.5:3

By volume, no wastage (M20 cross-check)

Dry D = 1.00 × 1.54 = 1.54 m³; ratio sum = 5.5
Cement = 1.54 ÷ 5.5 = 0.28 m³ → 403.2 kg → 8.06 → 9 bags
Raw 8.06 bags/m³ matches the published M20 ≈ 8 bags/m³ figure ✓
Sand = 1.54 × 1.5/5.5 = 0.42 m³ = 14.83 ft³ = 0.148 cube
Metal = 1.54 × 3/5.5 = 0.84 m³ = 29.66 ft³ = 0.297 cube
Water @ 0.50 = 0.50 × 403.2 = 202 litres

Column footing — 1:1:2 (Grade 25)

4 ft × 4 ft × 1.5 ft, 5% wastage

Wet V = 1.219 × 1.219 × 0.457 = 0.679 m³ (= 24 ft³)
After 5% wastage: 0.679 × 1.05 = 0.713 m³
Dry D = 0.713 × 1.54 = 1.098 m³; ratio sum = 4
Cement = 1.098 ÷ 4 = 0.2747 m³ → 395.6 kg → 7.9 → 8 bags
Sand = 1.098 × 1/4 = 0.274 m³ = 9.69 ft³ = 0.097 cube
Metal = 1.098 × 2/4 = 0.549 m³ = 19.4 ft³ = 0.194 cube

Frequently asked questions

Sources & references

Coefficients and the dry-volume factor on this page were last cross-checked against the sources above on 2026-07-11. Cement bag mass and density follow SLS 107; site units (cube = 100 ft³) follow standard Sri Lankan practice. Estimates are for material ordering — confirm structural mixes with your engineer.

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