Cement Calculator — How Many Bags Do You Need?
Estimate 50 kg cement bags two ways: from the area and thickness of a slab, screed or plaster — or directly from a concrete volume. Choose your mix ratio and get an instant answer.
Cement bags required
–
50 kg bags, rounded up
Wet volume
–
cubic metres
Dry material volume
–
wet volume × 1.54
Mix used
–
cement : sand : aggregate
How this cement calculator works
Cement is sold in 50 kg bags, but concrete and mortar are measured by volume — so you need a conversion between the two. This calculator takes either a surface area plus thickness (for slabs, screeds and plaster) or a concrete volume, converts it to dry material volume, takes cement's share according to your chosen mix, and divides by 0.0347 m³ (the volume of one 50 kg bag).
The formula
- By area: wet volume = area (m²) × thickness (m)
- By volume: wet volume entered directly (cft ÷ 35.3147 = m³)
- Dry volume = wet volume × 1.54
- Cement bags = (dry volume × cement share) ÷ 0.0347, rounded up
For mortar-only mixes like 1:4, the calculator treats the mix as cement + sand and computes cement's share of the two parts.
Worked example
A 100 sq ft floor screed, 2 inches thick, with 1:4 mortar. Area = 100 × 0.0929 = 9.29 m²; thickness = 2 × 0.0254 = 0.0508 m; wet volume = 0.47 m³; dry = 0.47 × 1.54 = 0.73 m³. Cement's share is 1/5 → 0.145 m³ ÷ 0.0347 = 4.19 → 5 bags.
Notes for Indian sites
Cement bags are standardised at 50 kg, and one bag holds about 0.0347 m³ — but never buy exactly the computed number; this calculator rounds up, and you should still keep one or two spare bags for touch-ups. Check the manufacturing date on every bag: cement older than 90 days can lose significant strength, and lumps in the bag are a warning sign. Store bags off the ground on a dry platform, stacked no more than 10 high, and use older stock first. If you are plastering, the standard 12 mm plaster with 1:4 mortar needs roughly 2 bags per 100 sq ft — a handy cross-check against your calculator result.
Frequently asked questions
How many cement bags are in 1 cubic metre?
One cubic metre of dry cement weighs about 1,440 kg, so it equals roughly 28.8 bags of 50 kg cement. But for concrete or mortar you don't buy 1 m³ of cement directly — the bags needed depend on the mix ratio, which is what this calculator works out.
What is the volume of one 50 kg cement bag?
One 50 kg bag of cement occupies about 0.0347 cubic metres (34.7 litres), based on cement's bulk density of 1,440 kg/m³. This calculator uses that figure to convert cement volume into bag counts.
How much cement is needed for 100 sq ft of plaster?
For 100 sq ft of plaster at 12 mm thickness with 1:4 mortar, you need roughly 0.17 m³ of dry mortar, which works out to about 1 bag of cement — but order 2 bags to be safe, since plaster wastage is high.
How many cement bags per cubic metre of 1:2:4 concrete?
About 7 bags. 1 m³ of wet concrete × 1.54 dry factor = 1.54 m³ of dry material; cement's 1/7 share is 0.22 m³, and 0.22 ÷ 0.0347 ≈ 6.34, which rounds up to 7 bags of 50 kg cement.
Should I round cement bags up when ordering?
Yes. Running out of cement mid-pour ruins a slab or wall section, and a spare bag keeps for months if stored dry. This calculator always rounds the bag count up to the next whole bag.