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Masonry · sand · cement · lime
How much sand and cement for mortar?
Straight mortar quantities, either from a volume or from a unit count. The mix presets are the ones off the old sheet: below DPC inside and out, above DPC inside and out.
1
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
2
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
How this one works
From a volume: dry volume = wet × 1.3, split by the ratio, converted to weight
From units: sand = units × sand per unit, which is the old sheet’s chain
Cement = sand ÷ sand parts × cement parts
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
Rate
Default
Why
Sand density
1.6 t/m³
Dry-to-wet factor
1.3
Dry sand and cement to mixed mortar.
Bag size
25 kg
Sand bulk bag
0.85 t
A worked example
With the defaults the page opens on:
What are you starting from? A volume of mortar
How much mortar? 1 cubic metres
How many bricks or blocks? 1500 number
Brick or block? Brick — 1.0 kg sand each
Which mix? 3:1 — below DPC
Spare for waste 10 per cent
Mix 3:1
Waste allowance: 10 %
Building sand: 1.72 t— 1,716 kg
Sand bulk bags: 3 bags — 1.7 / 0.85 tonnes a bag
Cement: 23 bags— 572 kg ÷ 25 kg
Hydrated lime: none — use a plasticiser
Covers roughly: 29 m² brickwork — at 60 bricks/m², 1 kg sand each
or: 95 m² blockwork — at 10 blocks/m², 1.8 kg each
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How much mortar per 1,000 bricks?
About a tonne of building sand at 1 kg per brick, before waste. Blocks take about 1.8 kg each. Pick the unit route, enter the count, and the cement and lime follow from the mix.
Which mortar mix should I use?
Richer below DPC where it stays wet (3:1), softer above so the mortar fails before the brick does (4:1:1 internal, 5:1:1 external). The presets are the ones from the old site sheet; the right mix for a particular wall is the specification’s call.
Why 10% waste on mortar?
It is the easiest material on site to waste - what goes off on the spot board. 10% is the default; change it.
What if I have no lime?
The 3:1 and 4:1 presets have none and the page says to use a plasticiser instead. Where a preset includes lime, it is shown in 25 kg bags.
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.
