Formula used
Net area = Gross area − Openings Wet volume = Net area × Layer thickness × Surface factor Dry volume = Wet volume × Dry-volume factor Sand volume = Dry volume × Sand parts ÷ Total ratio parts Cement volume = Dry volume × Cement parts ÷ Total ratio parts Sand order = Sand volume × Waste factor × Bulking factor Cement bags = Cement volume × Waste factor × Cement density ÷ Bag size
Dimensions first produce gross and net working areas. Layer thickness then converts area into wet material volume. Each selected factor adjusts the final purchase quantity correctly.
Masonry mode estimates mortar around bricks or blocks. It compares modular volume against actual masonry unit volume. Optional core intrusion adds mortar entering selected hollow cavities.
How to use this calculator
- Select plaster, rendering, screed, masonry mortar, or sand only.
- Choose dimensions, direct area, unit count, or wet volume.
- Enter all surfaces and subtract combined opening areas.
- Choose one coat or separate base and finishing coats.
- Set mix ratios, thicknesses, densities, and adjustment percentages.
- Add local prices for a complete project cost estimate.
- Calculate, review warnings, then export or copy results.
Example data
| Project | Area | Thickness | Ratio | Suggested adjustments |
|---|---|---|---|---|
| Internal plaster | 60 m² | 12 mm | 1:4 | 1.33 dry factor, 10% waste |
| External rendering | 85 m² | 15 mm | 1:4 | 1.05 surface factor, 12% waste |
| Floor screed | 40 m² | 40 mm | 1:5 | 1.33 dry factor, 8% waste |
| Brick mortar | 1,000 bricks | 10 mm joints | 1:6 | 20% bulking, 10% waste |
Important estimating guidance
Material densities vary with grading and moisture. Local sand testing provides a more reliable bulk density. Confirm supplier units before placing any final material order.
Bulking affects measured loose sand volume significantly. Moisture also increases delivered weight without adding dry solids. Field measurements should guide both adjustments during active work.
Plaster thickness changes rapidly on uneven masonry. A surface factor helps cover hollows and workmanship variation. Site trials remain essential for large or costly projects.
Frequently asked questions
What mix ratio should I use for plaster?
Common plaster ratios range from 1:3 through 1:6. Exposure, substrate, finish, and specifications affect the correct ratio. Follow approved drawings and local construction requirements first always.
Why is dry volume higher than wet volume?
Dry ingredients contain voids before mixing and compaction. Water and placement reduce those voids during mortar production. The dry factor compensates for this expected volume reduction.
What is sand bulking?
Moisture films separate sand particles and increase volume. The effect is strongest within certain moisture ranges. Measure bulking onsite when volume batching controls project materials.
Does the calculator subtract doors and windows?
Yes, each surface row accepts combined opening area. The calculator subtracts openings from the gross surface area. Enter deductions using the currently selected area unit carefully.
Can it calculate two-coat plaster?
Yes, select the two-coat arrangement in layer settings. Enter separate thicknesses and ratios for both coats. Results show each layer and the combined material requirement.
How does masonry mortar mode work?
It compares modular masonry volume against unit volume. The remaining volume represents mortar around joints and beds. Dimensions, joint thickness, and core intrusion percentage influence results.
Should hollow block voids be included?
Use this percentage only for mortar entering hollow cores. Leave zero when mortar remains on face shells. Core-fill percentage adds mortar entering selected hollow spaces directly.
Which sand density should I select?
Choose the condition matching your measured or supplied sand. Loose, compacted, and wet presets are approximate values. Custom laboratory or supplier density is usually more accurate.
Why are cement bags rounded upward?
Suppliers normally sell cement as complete bags. Rounding upward prevents purchasing less than the calculated requirement. Exact bags remain visible for planning and comparison purposes.
Can I use imperial units?
Yes, choose imperial units before entering project values. The form then uses feet, inches, and cubic feet. Results remain internally calculated using consistent metric conversions throughout.
Is this estimate suitable for purchasing?
It provides a structured planning estimate using your assumptions. Actual consumption varies with workmanship, waste, and site conditions. Verify major orders with drawings and field measurements onsite.