Understanding the Ballast to Cement Ratio
Ballast is a pre-mixed blend of sharp sand and gravel (typically a 2:1 gravel-to-sand ratio). When you buy bulk bags of ballast, you're getting the aggregate already combined — you just need to add cement and water. This makes it the easiest way to mix concrete for most DIY projects.
The most common ballast and cement ratio for general domestic work (paths, shed bases, fence posts) is 1 part cement to 4 parts ballast by weight. For structural work like lintels or load-bearing footings, use a stronger 1:3 ratio. If you're working with sand and cement alone (for mortar), use a 1:4 or 1:5 sand to cement mix ratio.
Reference Table — Bags Per Bulk Bag
| Mix Ratio |
Use Case |
25kg Bags |
20kg Bags |
| 1 : 3 (Strong) |
Structural, lintels, load-bearing |
12 bags |
15 bags |
| 1 : 4 (Standard) |
Paths, shed bases, fence posts |
9 bags |
11 bags |
| 1 : 5 (Lean) |
Backfill, non-structural bedding |
7 bags |
9 bags |
Frequently Asked Questions
How many bags of cement to a bulk bag of ballast?
For a standard 1:4 mix, you need approximately 9 × 25kg bags of cement (or 11 × 20kg bags) per bulk bag of ballast. A bulk bag weighs around 850kg, so at a 1:4 ratio you need about 212kg of cement.
How many bags of cement to a tonne of ballast?
For a 1:4 mix, you need 10 × 25kg bags of cement per tonne of ballast (250kg of cement). For a stronger 1:3 mix, you'd need about 14 × 25kg bags (333kg).
How many bags of cement to a bulk bag of sand?
For a standard 1:4 mix, roughly 9 × 25kg bags per bulk bag. If you're using sand alone without gravel, you're making mortar rather than concrete. For bricklaying mortar, a 1:4 or 1:5 cement-to-sand ratio is typical.
What's the difference between ballast and sand?
Ballast is a ready-mixed combination of sharp sand and gravel. It's convenient for making concrete because the sand and gravel are already blended. Sharp sand alone is used for mortar or combined separately with gravel for more precise concrete mixes.
How many bulk bags of ballast per cubic metre?
You need roughly 2 bulk bags of ballast plus the appropriate cement to make 1 cubic metre of concrete. A 1:4 mix needs about 1.7 bulk bags of ballast and 9 bags of cement per m³.
Can I use a 1:5 mix for a shed base?
A 1:5 mix is a lean mix best suited for non-structural work like backfill or bedding. For a shed base, a 1:4 standard mix is recommended as a minimum. If the shed will house heavy equipment, consider a 1:3 strong mix.
Is ballast the same as MOT Type 1?
No. Ballast is designed to be mixed with cement to make concrete. MOT Type 1 is a crushed stone sub-base material used underneath concrete slabs for drainage and stability. You lay MOT Type 1 first, compact it, then pour concrete made with ballast on top.
What is the sand and cement mix ratio for mortar?
The standard sand to cement ratio for mortar is 1:4 (1 part cement to 4 parts sharp sand) for general bricklaying, or 1:3 for a stronger mix below damp-proof course level. For rendering, use 1:5. Always use building sand (soft sand) for mortar, not sharp sand or ballast. Add plasticiser to improve workability.
How much ballast and cement do I need for 1 cubic metre?
For 1 cubic metre of concrete using a 1:4 ballast and cement mix, you need approximately 1.7 bulk bags of ballast (about 1,450kg) and 9 × 25kg bags of cement (225kg). The calculator above lets you work backwards from the amount of ballast you have to find out exactly how many bags of cement to add.
What is the best sand and cement mix for paths?
For concrete paths, use a 1:4 sand and cement mix with ballast (which already contains the right blend of sand and gravel). If mixing sand and gravel separately, use 1:2:3 (cement : sand : gravel). For a mortar bed under paving slabs, use a 1:4 sand cement mix with building sand. A 75–100mm thick slab is standard for garden paths.