Mortar Mix Calculator

What does a mortar mix ratio mean?

It's the proportion of cement to sand by volume. A 1:4 ratio means one part cement to four parts sand. That's the standard general-purpose mix for bricklaying and blockwork in the UK.

Which ratio should I use?

General purpose (1:4)

The go-to for most bricklaying and blockwork above DPC. If you're not sure, start here.

Strong (1:3)

You'll want this for load-bearing walls or anywhere that takes a battering from weather.

Paving (1:3)

Same ratio as strong, but it's the standard choice for bedding slabs and flagstones.

Render (1:5)

A weaker mix on purpose. Render needs to flex slightly with the wall underneath, so less cement is better here.

Where do these numbers come from?

Mixed mortar takes up less space than the dry ingredients that went into it. The calculator applies a bulking factor of 1.54 to account for that difference, then splits the dry volume by your chosen ratio. Cement density is taken as 1,440 kg/m³ and sand as 1,600 kg/m³. Water is worked out at a 0.5 water-to-cement ratio by weight.