Example Data Table
| Length (m) | Width (m) | Thickness (mm) | Ratio | Wastage (%) | Cement (kg) | Sand (m3) | Water (L) |
|---|---|---|---|---|---|---|---|
| 4 | 3 | 20 | 1:4 | 5 | 96.53 | 0.2681 | 48.3 |
Example assumes dry factor 1.33 and water-cement ratio 0.50.
Formula Used
- Area (m2) is calculated as Length x Width, or entered directly.
- Wet volume (m3) = Area x Thickness, where thickness is converted from mm to meters.
- Adjusted wet volume = Wet volume x (1 + Wastage%/100).
- Dry volume = Adjusted wet volume x Dry factor.
- Cement volume = Dry volume x CementPart / (CementPart + SandPart).
- Sand volume = Dry volume x SandPart / (CementPart + SandPart).
- Cement kg = Cement volume x Cement density.
- Bags (exact) = Cement kg / Bag size, and recommended bags are rounded up.
- Water (L) ~ Cement kg x Water-cement ratio.
How to Use This Calculator
- Select Input mode: use dimensions, or enter total area.
- Enter thickness for your mortar bed or surface render.
- Set wastage to cover spillage and uneven surfaces.
- Choose a mix ratio or switch to custom parts.
- Pick your bag size and confirm water-cement ratio.
- Optionally add prices to get a quick cost estimate.
- Press Calculate; then download CSV or PDF if needed.
Typical Mortar Thickness for Garden Work
Mortar demand changes sharply with thickness. Bedding for pavers or edging often sits between 10 and 25 mm, while thin renders and pointing are commonly 8 to 15 mm. This calculator converts millimeters to meters, multiplies by area, then adds your wastage percentage. Small thickness changes can add many kilograms of cement on larger patios. Measure thickness using a straightedge first.
Choosing a Cement-Sand Ratio
Mix ratio affects strength, shrinkage, and workability. For general garden brickwork and blockwork, 1:4 or 1:5 (cement:sand) is frequently used, while 1:3 is stronger for small repairs or high wear edges. A leaner 1:6 can suit low-load bedding. Use the custom option when you follow a site specification.
Why Dry Volume Is Higher Than Wet Volume
Dry ingredients occupy more space before mixing because voids between sand grains collapse once water and cement paste fill them. The dry volume factor, often around 1.27 to 1.33, scales adjusted wet volume into a realistic dry ingredient total. If sand is very well graded or moisture is high, a slightly lower factor may fit better.
Interpreting Bags, Volume, and Costs
The calculator splits dry volume by mix parts to estimate cement and sand volumes, then converts cement volume to kilograms using bulk density (typically about 1440 kg/m3). It reports exact bags and rounds up to whole bags for purchasing. For example, 12 m2 at 20 mm equals 0.24 m3 wet; with 5% waste and a 1.33 factor, dry volume is about 0.335 m3. Optional pricing estimates costs for cement, sand per cubic meter, and water per cubic meter without locking to any currency.
Water Demand and Workability Notes
Water is estimated from the water-cement ratio, usually 0.45 to 0.60 for workable mortar. Lower values reduce shrinkage but may be harsh to place; higher values improve flow but can weaken mortar. Adjust gradually and keep sand moisture in mind. For best results, mix consistently, avoid re-tempering, and cure damp surfaces in hot weather.
FAQs
1) Should I use wet or dry volume for ordering materials?
Order materials from the dry volume outputs. Wet volume describes placed mortar; dry volume accounts for bulking and voids so cement and sand quantities match real batching and purchasing.
2) What wastage percentage is reasonable for garden jobs?
For neat, accessible areas, 5% is common. Use 8% to 12% for uneven bases, small batches, or complex edges where trimming and spillage increase losses.
3) Which ratio is best for pointing joints outdoors?
Many outdoor pointing jobs use 1:4 or 1:5 for durability and workable joints. If joints are thin or exposed to heavy wear, a slightly richer mix may be chosen by specification.
4) Why does the bag recommendation round up?
Cement is normally purchased in whole bags. Rounding up avoids running short mid-job and helps keep the mix consistent across batches, especially when wastage is uncertain.
5) Can I enter feet and inches instead of meters?
This version calculates in metric. Convert dimensions to meters and thickness to millimeters before entry. The results also show cubic feet equivalents to help with ordering and comparison.
6) Does the water estimate include moisture already in the sand?
No. The calculator assumes dry materials. If sand is damp, reduce added water gradually during mixing. Aim for a workable, cohesive mortar that holds shape without bleeding.