Calculator Inputs
Example Data Table
| Scenario | Inputs | Key Outputs |
|---|---|---|
| Plastering (typical) |
Area: 20 m² Thickness: 12 mm Ratio: 1:4 Wastage: 5% Dry factor: 1.33 |
Cement: ~115 kg (varies) Bags (50 kg): ~2.30 Sand: ~0.268 m³ |
| Known mortar volume |
Mortar volume: 0.25 m³ Ratio: 1:5 Wastage: 7% Dry factor: 1.33 |
Cement and sand split by ratio. Dry volume increases by factor and wastage. Bag counts follow the selected bag size. |
Example values are illustrative. Actual site results can differ due to sand moisture, surface level, and workmanship.
Formula Used
1) Convert to wet mortar volume: Vwet = Area × (Thickness ÷ 1000) or use your known Vwet.
2) Add wastage: Vw = Vwet × (1 + W% ÷ 100)
3) Convert to dry volume: Vdry = Vw × Dry Factor
4) Split by mix ratio (cement:sand = C:S): Vcement = Vdry × C ÷ (C+S) Vsand = Vdry × S ÷ (C+S)
5) Convert volumes to weights and bags: kg = Volume × Density Bags = Cement kg ÷ Bag Size
How to Use This Calculator
- Select a calculation method: Area & thickness or Known mortar volume.
- Enter area and thickness, or enter the mortar volume directly.
- Set the mix ratio, wastage allowance, and dry volume factor.
- Review cement density and bag size to match your supply.
- Click Calculate to see results above the form.
- Use the download buttons to export CSV or PDF.
Mortar Cement Planning Guide
Accurate mortar planning improves productivity, reduces waste, and helps maintain consistent masonry quality. This calculator estimates cement, sand, and water from either (a) surface area and thickness or (b) a known wet mortar volume. It then applies a wastage allowance and converts wet volume to dry ingredients using a dry-volume factor. Finally, the dry volume is split by your selected cement-to-sand ratio to provide practical purchase quantities such as cement bags and bulk sand volume.
On site, the same “1:4” ratio can behave differently depending on sand grading, moisture, and how aggressively the mix is worked. Start with a sensible water-cement ratio (often 0.45–0.60) and adjust gradually to achieve the required workability without making the mix overly wet. Excess water can cause shrinkage and weaker finishes, while very dry mixes can reduce bond and make placement difficult. The default cement density and sand density values are common bulk figures; update them if your supplier provides tested densities, especially for damp sand or blended materials.
A professional estimate also considers small losses: mortar left in the pan, spillage during transport, and uneven backgrounds that demand extra thickness. Using a modest wastage percentage (for example 5–10%) typically aligns calculations with real consumption. For repeatable results, measure thickness at multiple points, average the readings, and keep the chosen ratio consistent across the work area.
Worked example (plastering)
Suppose you are plastering 20 m² at 12 mm thickness using a 1:4 mix, 5% wastage, and a 1.33 dry-volume factor. Wet volume is 20 × (12 ÷ 1000) = 0.24 m³. With wastage it becomes 0.252 m³, and dry volume becomes 0.252 × 1.33 = 0.335 m³. Cement share is 1/(1+4) of dry volume, and sand share is 4/(1+4). Converting cement volume to weight using 1440 kg/m³ gives the cement kilograms and bag count, while sand volume can be converted to an estimated sand weight using the chosen sand density.
Use the example table above as a quick reference and adjust inputs to match your project.
FAQs
1) What dry volume factor should I use for mortar?
Many site estimates use 1.30–1.35. It accounts for bulking and voids when converting wet mortar to dry ingredients. If you have measured consumption on similar work, use that value for better accuracy.
2) Is the mix ratio by weight or by volume?
This calculator treats the cement:sand ratio as a volume ratio, which matches common site practice using boxes or shovels. Weight results are derived afterward using the selected material densities.
3) Why does my site need more mortar than the estimate?
Extra consumption often comes from uneven surfaces, thicker application, spillage, and mortar left in tools. Increase wastage percent, verify thickness at multiple points, and ensure the correct area is measured.
4) How accurate is the water estimate?
It is an approximation based on the water-cement ratio. Real water demand changes with sand moisture, temperature, admixtures, and desired workability. Add water slowly and stop once the mix reaches the required consistency.
5) Can I use this for pointing or bedding mortar?
Yes. Use area and thickness if you can estimate the coverage layer, or switch to known mortar volume if you can approximate the mixed quantity. Adjust the ratio to match your specification.
6) Should I change cement density and sand density?
Keep defaults for general estimating, but change them if your supplier provides tested bulk densities. Damp sand can be heavier, and different cement brands can vary slightly, affecting weight-based ordering.
7) What is a practical rounding method for ordering?
Round cement to the next full bag and add one spare bag for small jobs. Round sand volume up slightly to cover handling losses. For large projects, order in batches and compare actual usage weekly.