Cement Calculator

Ordering cement for a plaster or screed job usually comes down to one practical question: how many bags for this area? The answer depends on four things — the area, the thickness, the cement-to-sand ratio and the size of the bag — and while the arithmetic is simple, getting it wrong means a mid-job run to the supplier or a bag too many left in the yard.

Cement Calculator converts any floor or wall area and thickness into an exact number of cement bags, in both slab mode (concrete mixes M5 to M25) and plaster-screed mode (cement-sand ratios 1:3 to 1:6). It reports bags per square foot, bags per 100 sq ft, the sand volume, and the dry-mix maths behind each figure, in imperial or metric units.

Underneath the inputs is a guide to plaster and screed thicknesses, cement-sand ratios and the dry factors that make estimates honest. Everything runs in your browser; nothing is uploaded.

• Bags per square foot: The headline figure — exactly how many bags of cement your area and thickness take.
• Two working modes: Concrete slab mode for M5 to M25 mixes, and plaster-screed mode for cement-sand ratios 1:3 to 1:6.
• Any area and thickness unit: Length and width in six units, thickness in inches, millimetres, centimetres, metres or feet.
• Area in sq ft always shown: Square feet, square metres and acres-of-constant conversion so the per-square-foot figure reads clearly.
• Bag size choice: 25, 40 and 50 kg bags with the order quantity rounded up to whole bags.
• Correct dry factor: 1.33 for mortar and screed, 1.54 for concrete, both adjustable with a waste allowance.
• Sand breakdown: The sand volume in cubic metres and kilograms that pairs with the cement.
• Live maths line: Shows wet volume, dry factor and ratio split so every number can be verified.
• Full report & export: Copy or download the estimate as text, CSV or JSON for your quote.
• Learning guide: Plaster thicknesses, mortar ratios, screed guidance and yield-per-bag table built into the tool.

1. Choose the mode. Slab for concrete floors, plaster for wall and ceiling coats, screed for floor bedding.
2. Enter the length and width. The unit selector applies to both; the area appears in square feet automatically.
3. Set the thickness. Use its own unit — 0.5 inches or 12 mm are typical plaster thicknesses.
4. Pick the mix ratio. 1:4 for general plaster and screed, 1:3 for richer work, M15 or M20 for concrete slabs.
5. Select the bag size and waste. 50 kg is standard; 5 percent waste is a sensible default.
6. Read the bag count. Total bags, bags per square foot and per 100 sq ft all appear instantly.
7. Note the sand volume. The paired sand in cubic metres and kilograms is shown for ordering together.
8. Export the report. Copy or download the summary as text, CSV or JSON.

Example 1 — Wall plaster. A wall 20 ft by 10 ft plastered 12 mm thick at 1:4 takes about 2.24 m³ dry mortar and roughly 2.4 bags of 50 kg cement — about 0.2 bags per 100 sq ft per millimetre of thickness.

Example 2 — Floor screed. A 150 sq ft floor screeded 1 inch thick at 1:4 needs about 0.32 m³ dry mix and roughly 1.8 bags of cement, with about 0.26 m³ of sand.

Example 3 — Concrete slab. A 100 sq ft slab 4 inches thick (about 0.31 m³) at M15 takes about 2 bags of 50 kg cement, with sand and coarse aggregate from the ratio.

Example 4 — Checking a quote. A contractor quotes 15 bags for a 500 sq ft interior. At 12 mm and 1:4 the calculator gives about 12 bags, so the difference flags an unusually thick or wastage-heavy estimate worth questioning.

Example 5 — Bulk order. Plaster the whole ground floor of 900 sq ft at 12 mm, 1:4. The total is about 21 bags of cement — order 24 to round to full pallets and allow for waste.

• Order the right number of bags: Convert any area and thickness to an exact bag count, including per-square-foot figures.
• Plaster, screed or concrete: One tool handles wall plastering, floor screeding and concrete slabs with the correct dry factors.
• Work in the units you use: Mix imperial area with metric thickness and still get sq-ft-per-bag numbers.
• Pair the sand automatically: The matching sand volume means one clean order, not two separate guesses.
• Verify the maths: The working line shows wet volume, dry factor and ratio, so nothing is a black box.
• Export the quote: Text, CSV and JSON summaries drop straight into orders and spreadsheets.
• Free and private: No account, no watermark, nothing uploaded.