How Much Gravel Is in a Bulk Bag? UK Weights, Coverage and Prices

Bulk bags (also called dumpy bags, tonne bags or jumbo bags) are sold by weight, not by volume. There's no legal standard fill, so each merchant sets its own:

• Travis Perkins lists its 20mm gravel and shingle bulk bag at 800 kg, "can range up to 850kg depending on moisture content".
• MKM Building Supplies and TW Aggregates both list their 20mm gravel bulk bags at about 850 kg.
• A few suppliers sell a "jumbo" or true tonne bag at around 1,000 kg, and some sell half bags of about 450 kg.

So "tonne bag" is a name, not a promise. Before you compare prices, check the weight printed on the product page.

Takeaway: assume 850 kg unless the merchant states otherwise, and treat 1,000 kg as the exception.

Coverage depends on two things: the stone's density and the depth you lay it at. The formula is simple:

Coverage (m²) = bag weight (tonnes) ÷ density (t/m³) ÷ depth (m)

Using the same densities as our gravel calculator (dry, loose stone):

Notice the slate row. An 850 kg bag of slate covers about 24% more ground than an 850 kg bag of gravel, because slate is lighter per cubic metre. Most merchant coverage figures quote one number for every stone, which overstates gravel and understates slate.

Takeaway: for 20mm gravel at 50mm deep, plan on about 10 m² per bag. For a 30mm decorative border, closer to 17 m².

There are 40 bags of 25 kg in a tonne, and 50 bags of 20 kg. An 850 kg bulk bag holds the same stone as 34 small 25 kg bags.

One 25 kg bag of 20mm gravel is about 0.016 m³, which covers roughly 0.3 m² at 50mm. That's fine for topping up a planter or a short path edge. Past about 3 m², small bags cost more, take more trips and leave you with a pile of plastic to get rid of.

Takeaway: if you need more than 12 small bags, price up a bulk bag instead.

Prices vary by region, stone and delivery distance, so treat these as a guide:

The second row is the trap. Two bags at the same shelf price can differ by £4 a tonne simply because one is filled to 800 kg and the other to 850 kg. Always divide the price by the stated weight.

Most merchants add a delivery charge per drop, and bulk bags come off a lorry-mounted crane. Check the crane can reach where you want the bag, because moving 850 kg by hand means about 34 barrow loads at 25 kg each.

Takeaway: compare price per tonne, not price per bag, and ask about the delivery charge before you order.

Loose loads are tipped straight off the lorry. Gravel Base says a loose load tipper starts at roughly 10 tonnes and needs 3.5 m of access and somewhere firm to tip. That makes loose tipping cheaper per tonne, but only if you need a lot and have the space.

Takeaway: bags win for a garden path or a small driveway top layer, while a tipper wins for big sub-base jobs.

Priya wants to gravel a 6 m by 4.5 m driveway in 20mm gravel at 50mm deep, on top of a new MOT Type 1 sub-base 150mm deep.

Top layer (20mm gravel):

1. Area: 6 × 4.5 = 27 m²
2. Volume: 27 × 0.05 = 1.35 m³
3. Weight: 1.35 × 1.60 = 2.16 tonnes
4. Add 5% for levelling and spillage: 2.16 × 1.05 = 2.27 tonnes
5. Bulk bags at 850 kg: 2.27 ÷ 0.85 = 2.67, so order 3 bags
6. Cost at £54 a bag: 3 × £54 = £162, plus delivery

Three bags give her 2.55 tonnes, about 0.28 tonnes spare for topping up after the first winter.

Sub-base (MOT Type 1 at 2.00 t/m³ compacted):

1. Volume: 27 × 0.15 = 4.05 m³
2. Weight: 4.05 × 2.00 = 8.1 tonnes
3. Add 5%: 8.1 × 1.05 = 8.51 tonnes
4. In 850 kg bulk bags that's 8.51 ÷ 0.85 = 10.01, so 11 bags

Eleven bags of sub-base is where a single loose load makes more sense. So the sensible order is one loose tipped load of Type 1 and three bulk bags of gravel. You can check both quantities in seconds with our gravel calculator and price the whole job with the driveway cost calculator.

Takeaway: split the order. Use a loose load for the heavy sub-base and bulk bags for the finish.

In practice, most UK landscapers find a bag of 20mm gravel covers slightly less than the table says. There are three reasons:

• Moisture. Stone sold by weight includes the water in it. A bag that's sat in the yard through a wet week gives you a little less stone.
• Uneven ground. Every 10mm of extra depth across 10 m² swallows another 0.1 m³, which is 160 kg of gravel.
• Settling. Gravel beds down under foot and car traffic, so a 50mm layer can look like 40mm after a few months.

That's why we add 5% and round up to the next whole bag.

Takeaway: order the extra bag now. A second delivery for one bag usually costs more than the bag itself.

If you're laying topsoil or turf on the same project, the topsoil calculator converts your area into bulk bags too, using a 0.6 m³ bag size.

Takeaway: don't go deeper than 50mm on a driveway surface. Deeper gravel shifts under tyres and gets rutted.

Most UK bulk bags weigh 800 to 850 kg. Travis Perkins states 800 kg, rising to 850 kg with moisture, and MKM states 850 kg. Some suppliers sell a jumbo bag of about 1,000 kg, but that's the exception.

An 850 kg bag of 20mm gravel covers about 10.6 m² at 50mm deep, 13.3 m² at 40mm and 17.7 m² at 30mm. Slate chippings go further, at about 13.1 m² per 850 kg bag at 50mm.

Forty. A 20 kg bag size needs 50 bags per tonne. An 850 kg bulk bag equals 34 bags of 25 kg.

Usually not. "Tonne bag" is the name of the bag, and most are filled to 800 or 850 kg. Check the weight on the product listing and compare prices per tonne.

Loose is cheaper per tonne, but loads usually start at about 10 tonnes and need around 3.5 m of access. For under 5 tonnes, bulk bags are normally the better buy once delivery is included.

Multiply the area by 0.05 (for 50mm) and by 1.6 to get tonnes of 20mm gravel, then add 5%. A 27 m² driveway needs about 2.27 tonnes, or three 850 kg bulk bags. For the full method, read how much gravel do I need.

The figures in this guide are estimates based on typical UK densities and published merchant bag weights as of October 2026. Stone density varies by quarry and moisture. Always check the stated bag weight with your supplier. For driveways, check drainage and any planning requirements with your local council or a qualified groundworker before you order.