Question 1

How much gravel do I need per m²?

Accepted Answer

The amount depends on depth. For decorative gravel at 40mm depth, you need approximately 70kg per m² (1.6 tonnes per m³ × 0.04m). For a gravel driveway at 75mm depth, you need approximately 130kg per m². Our calculator works this out automatically based on your chosen depth and aggregate type.

Question 2

What is the difference between a bulk bag and a tonne?

Accepted Answer

A standard bulk bag (jumbo bag) holds approximately 850kg of aggregate, which is about 0.5m³. This means a bulk bag is NOT a tonne — you need roughly 1.2 bulk bags to make 1 tonne. Always check with your supplier as bag sizes can vary. Loose tipped deliveries are usually cheaper per tonne than bulk bags.

Question 3

What depth of gravel do I need for a path?

Accepted Answer

For a garden path, 40-50mm of gravel over compacted sub-base is standard. For a gravel driveway, use 50-75mm of gravel over at least 150mm of compacted Type 1 MOT sub-base. Always use a geotextile membrane between layers to prevent mixing and weed growth.

Question 4

How many 25kg bags per m²?

Accepted Answer

At 50mm depth with standard 20mm gravel: approximately 3.5 bags per m² (1,750 kg/m³ × 0.05m = 87.5 kg per m² ÷ 25 = 3.5 bags). At 25mm depth it halves to about 1.75 bags per m². 25kg bags are only economical for small areas — bulk bags or loose tipped are far cheaper for larger projects.

Question 5

How do I calculate aggregate for an L-shaped area?

Accepted Answer

Split the shape into rectangles, run the calculator once for each rectangle and add the tonnages together. Volumes of loose material are simply additive, so the summed total is exact, not an approximation, and unlike slabs or boards there is no cutting penalty where the sections meet. The sections can even use different depths, for example a driveway leg at 150mm and a path leg at 50mm. One tip on bags: add the tonnage figures first and convert the combined total to bulk bags or 25kg bags at the end, because each individual run rounds its bag count up and summing rounded counts can over-order by a bag.

Question 6

Do I need membrane under gravel?

Accepted Answer

Yes, always lay a geotextile weed membrane under gravel. This prevents weeds growing through, stops the gravel sinking into the soil, and keeps layers separated. Use heavy-duty landscape fabric (100g/m² minimum), overlapping joins by at least 150mm.

Aggregate Calculator — How Much Gravel, Sand or Stone Do I Need?

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