Masonry Mortar Mix Calculator
Cement, sand and water for M5-M15 mortar by volume, with a batch sheet.
Quick answer
With the default inputs: Mortar volume 1 m³ · Mortar grade M7.5 · Cement class 32.5 etc.Cement 220 kg
Edit the inputs below to recalculate.Inputs
Result
Cement
220kg
| Cement per m³ | 220kg/m³ |
| 50 kg bags | 5bags |
| Sand (dry) | 1.02m³ |
| Sand (as delivered) | 1509kg |
| Water to add | 250kg |
| Sand per 50 kg cement | 343kg |
| Water per 50 kg cement | 56.9kg |
| Ratio cement : sand | 1 : 6.7 |
Cement contents are common field values and drop when lime putty is used. Added water is net of sand moisture — the step most often skipped on site, and the usual cause of weak mortar.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Cement | M = reference by grade × volume |
| 42.5 class | reference × 0.88 |
| Sand | V = 1.02 × mortar volume (loose) |
| Water to add | W = 280 × V − moisture in sand |
| Strength | 70.7 mm cube at 28 days |
1 m³ of M7.5 with 32.5 class cement and 2% sand moisture: 220 kg cement (5 bags), 1.02 m³ of dry sand around 1479 kg and about 250 kg of added water — a ratio near 1 : 6.7.
How to work it out
- Look up the baseline cement content by mortar grade: about 190 kg/m³ for M5, 220 for M7.5, 260 for M10 and 320 for M15, with 32.5 grade cement.
- Adjust for cement grade: with 42.5 cement, multiply the baseline by about 0.88.
- Sand is taken as 1.02 m³ loose per m³ of mortar, allowing for moisture and compaction.
- Water follows the required consistency: 280-320 kg/m³ for a masonry mortar at 50-70 mm slump.
- Deduct the water in the sand: actual water = total water − sand weight × moisture content.
Where it goes wrong
- Mixing by volume ratios like 1:3 or 1:6 — those are historical habits with no strength guarantee; proper work needs weight batching and trial mixes.
- Using one mix for M5 and M7.5 — 30 kg/m³ of cement separates the grades, and masonry capacity differs accordingly.
- Not testing sand moisture — it swings 2-8% from the stockpile, and unadjusted water makes the mortar wet and weak.
Material and cost
Ready-mixed M7.5 masonry mortar runs 280-360 per m³; site mixing costs 200-260 per m³ in materials but adds labour and waste. Ready-mixed saves labour and holds quality, which is why it is now the norm.
On site
- Use mortar as mixed: cement mortar within 3 hours and composite mortar within 4; discard beyond that.
- Take one set of test cubes per inspection lot (same mix, same grade, up to 250 m³ of masonry).
- Adjust consistency with the weather: stiffer in summer (70-80 mm), wetter in winter (50-60 mm).
Basis
- JGJ/T 98-2010 Specification for mix proportion design of masonry mortar
- GB 50203-2011 Code for acceptance of masonry construction, Chapter 4 (mortar)
- GB/T 25181-2019 Ready-mixed mortar
FAQ
What does M7.5 mean?
A mean compressive strength of at least 7.5 MPa for 70.7 mm cubes cured 28 days. It is a mean, not a characteristic value, and the specimen is a 70.7 mm cube — not the 150 mm cube used for concrete. Mortar test results scatter far more than concrete.
Why deduct the water in the sand?
Sand at 2% moisture brings about 30 kg of water per cubic metre; adding the full 280 kg pushes the water-cement ratio over 10% high, costing 15-20% strength and increasing shrinkage. In the rainy season sand can reach 8%. Measure moisture each shift by drying or a rapid meter.
Is more cement always better in mortar?
No. Excess cement increases shrinkage and cracking, mismatches brick movement and costs more. The key property is workability — water retention and consistency — which lime putty or fly ash improve better than extra cement. The code sets a minimum cement content but also discourages over-strong mortar in masonry.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Masonry Mortar Mix Calculator. 2026-10-25. https://jianzhujisuan.com/en/masonry-mortar-mix
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.