Mortar calculator — how much sand & cement do I need?
Enter the length and height of your wall and pick what you're laying. The calculator works out the building sand and Portland cement bags for the mortar — whether you're pointing a garden wall or bedding a run of blocks.
Enter the wall size and what you are laying. We work out the building sand and cement bags for the mortar, based on 10mm joints.
Mix ratiosand : cement
Waste
7 × 25kg cement
for 793 bricks · 12.0m² wall
Building sand793 kg — 1 bulk bag or 32 × 25kg bags
Portland cement7 × 25kg bags
Water & plasticiseradd gradually to a workable — not wet — mix
Typical trade allowances: about 60 bricks or 10 blocks per m² with 10mm joints, and roughly 1 tonne of sand per 1,000 bricks. A 5:1 mix suits most facing work; use 4:1 for retaining walls or below damp-proof course. Guide only — confirm with your bricklayer.
How it works
1Measure the wall — length and height in metres. Measure awkward sections separately and add them together.
2Pick what you're laying. A standard UK facing brick works out at about 60 bricks per square metre with 10mm joints; 100mm concrete blocks about 10 per square metre. Double-skin or cavity walls need twice the mortar of a single skin.
3Choose your mix ratio. 5:1 sand to cement suits most above-ground facing brickwork. Use 4:1 for retaining walls, chimneys or anything below the damp-proof course; 6:1 is fine for internal blockwork.
4Add a waste allowance. Most bricklayers allow 5–10% for mortar lost to spills, weather and mixing board leftovers.
5Order the materials. The calculator gives building sand (bulk bags or 25kg bags) and 25kg Portland cement bags — take the list across to the price comparison to find the cheapest merchant near you.
Common mortar quantities
Garden wall, 5m × 1m single skin — about 300 facing bricks, roughly 300kg of building sand and 3 × 25kg bags of cement at 5:1.
Garden wall, 5m × 1m double skin — around 600 bricks, roughly 600kg of sand and 6 × 25kg bags of cement at 5:1.
Garage wall, 6m × 2.4m in 100mm blocks — about 145 blocks, roughly 435kg of sand and 4–5 × 25kg bags of cement at 5:1.
Which mix ratio should I use?
4:1 — stronger mix for retaining walls, chimneys, coping stones and work below the damp-proof course.
5:1 — the everyday choice for most external facing brickwork and blockwork.
6:1 — suitable for internal blockwork and non-loadbearing walls where a softer mix is fine.
Add a squirt of plasticiser to make the mix workable without making it sloppy — and never lay bricks in frost or pouring rain.
Take your quantities across to Price Planter and compare them across UK builders' merchants — including whether splitting the order across two merchants works out cheaper.
Mortar quantities use typical trade allowances: about 60 bricks or 10 blocks per m² with 10mm joints, and roughly 1 tonne of building sand per 1,000 bricks. They are a guide only — confirm quantities with your bricklayer and merchant before ordering.