How to Calculate How Much Aggregate You Need (With Examples)

12 May

Whether you’re laying a new driveway, preparing a foundation base, or building a garden path, knowing how much aggregate to order is essential. Too little, and you risk delays. Too much, and you waste money. Fortunately, calculating what you need is simple once you know the right formula.

Here’s a quick guide — with examples — to help you get it right the first time.

🧮 The Basic Formula for Aggregate Volume

To calculate the amount of aggregate you need, use this formula:

Length (m) × Width (m) × Depth (m) = Volume (m³)

Then, convert cubic metres into tonnes. On average:

1 cubic metre of aggregate = approx. 1.5 tonnes
(Depending on the material and moisture content)

📏 Example 1: Sub-base for a Patio

Project: 4m x 3m patio with a 100mm (0.1m) sub-base
Calculation:
4 × 3 × 0.1 = 1.2m³
1.2m³ × 1.5 = 1.8 tonnes

👉 You’ll need approx. 1.8 tonnes of MOT Type 1 or crushed concrete.

📏 Example 2: Gravel Driveway Top Layer

Project: 10m x 3m driveway with a 50mm (0.05m) decorative gravel layer
Calculation:
10 × 3 × 0.05 = 1.5m³
1.5m³ × 1.5 = 2.25 tonnes

👉 You’ll need approx. 2.25 tonnes of decorative gravel or ragstone chippings.

📏 Example 3: Raised Bed Fill

Project: Filling a 2m x 1m x 0.3m raised bed with topsoil
Calculation:
2 × 1 × 0.3 = 0.6m³
0.6m³ × 1.5 = 0.9 tonnes

👉 You’ll need approx. 0.9 tonnes of screened topsoil.

🧠 Tip: Always Round Up

Aggregate compacts and settles. Always round up your order slightly to account for this and for uneven ground.

🧮 Want to Skip the Maths?

Use our free online tool to get an instant estimate tailored to your project:

➡️ Try the Kernahans Materials Calculator

It’s fast, easy, and helps make sure you order the right amount — whether it’s for soil, gravel, crushed concrete, or any other material we supply.

Need Aggregate Delivered?

We supply a full range of aggregates across Kent — including MOT Type 1, crushed concrete, topsoil, sand, gravel, and more. Whether you need loose loads tipped off or bulk bags delivered, we’ve got you covered.

📍 Local delivery available
🪨 Loose or bagged options
📞 Friendly advice if you're unsure what you need

➡️ Contact us today to book your delivery or learn more about our aggregate products.