How Many Tonnes of Gravel Are in a Bulk Bag?
Quick answer: A UK “bulk bag” (also called a jumbo, dumpy, or tonne bag) typically holds around 0.8 tonnes of gravel — often 800–850kg, not a full tonne, despite the “tonne bag” nickname. One bulk bag covers roughly 9–10 square metres at 50mm deep. Always check your supplier’s stated weight, as it varies by material and merchant, and denser aggregates can be closer to a full tonne in the same bag.
The word “tonne bag” causes more over- and under-ordering than almost anything else in landscaping, because most bulk bags don’t actually contain a full tonne. Get this wrong and you either pay for more bags than you need or come up short mid-job. This guide clears up what a bulk bag really holds, how far it goes at different depths, how to convert correctly between bags and tonnes, and when bulk bags beat small bags on price. Use the calculator above to get your bag count.
The “tonne bag” myth
Bulk bags are often nicknamed “tonne bags,” but that refers to the bag’s maximum capacity, not what’s inside. In practice, suppliers commonly fill them to around 0.8 tonnes of gravel or aggregate — a standard UK bulk bag holds roughly 800–850kg of 20mm gravel, which is about 0.5 m³. Some suppliers sell “half bulk bags” of around 0.4 tonnes too. Heavier aggregates like crushed granite can weigh closer to a full tonne in the same volume, because they’re denser.
So if a calculation tells you “you need 2 tonnes,” that is not the same as “2 bulk bags.” At 0.85 tonnes per bag, 2 tonnes is closer to 2.5 bags — so you’d order three. Ordering by the bag without checking the weight is how people come up short.
How far does one bulk bag go?
Coverage depends on depth. For a bulk bag holding around 0.85 tonnes:
| Depth | Approx. coverage per bulk bag |
|---|---|
| 25mm (1in) | ~16–20 m² |
| 40mm | ~10–12 m² |
| 50mm (2in) | ~9–10 m² |
| 75mm | ~5–7 m² |
Lay it deeper and one bag covers less area. For a decorative gravel top layer, 50mm is standard, so plan on roughly 9–10 m² per bag. For a shallower decorative border at 30–40mm, one bag stretches further.
Converting tonnes, bags, and volume
The chain runs: area × depth = volume → volume × density = tonnes → tonnes ÷ bag weight = bags.
The two figures that trip people up are the density (different aggregates weigh different amounts per cubic metre, so the same volume gives different tonnages — pea shingle, slate, and MOT Type 1 all differ) and the bag weight (how many tonnes your supplier actually puts in a bag, usually around 0.8). Get both right and the bag count is accurate. Assume “1 bag = 1 tonne” and you’ll be roughly 20% short.
Bulk bags vs small bags: which is cheaper?
Once you’re buying more than a few hundred kilos, bulk bags almost always beat small handy bags on price per kilo. Small bags (usually 20–25kg) are convenient for tiny jobs or topping up, but for a driveway or a path they work out expensive — a single bulk bag replaces roughly 35–40 small bags, usually at a much lower price per kilo.
For big jobs, loose tipped delivery by the tonne can be cheaper still, if you have somewhere for the lorry to tip it and don’t mind barrowing it into place. So the rough order of cost per kilo, cheapest first, is: loose tipped load, then bulk bags, then small bags. Choose based on the size of your job and how the material can be delivered and stored.
Common mistakes to avoid
The biggest mistake is treating “tonne bag” literally and assuming one bag is a full tonne — it’s usually about 0.8. The second is buying small bags for a large job, which costs far more per kilo. The third is using a generic density and getting the tonnage wrong for your specific material. And the fourth is not checking your supplier’s actual bag weight, which varies between merchants and materials. A quick look at the product page settles it.
Frequently asked questions
Is a bulk bag of gravel a tonne?
Usually not quite — most bulk bags hold around 0.8 tonnes (often 800–850kg) despite the “tonne bag” nickname. Denser aggregates like crushed granite can be closer to a full tonne in the same volume. Always check your supplier’s stated weight.
How much area does a bulk bag of gravel cover?
Around 9–10 m² at 50mm deep. Coverage increases at shallower depths — roughly 10–12 m² at 40mm and 16–20 m² at 25mm — and decreases at deeper ones.
How many small bags equal a bulk bag?
A bulk bag holds roughly 35–40 standard 20–25kg bags, and works out much cheaper per kilo for larger jobs. Small bags are best kept for tiny projects or topping up.
How do I convert tonnes of gravel to bulk bags?
Divide the tonnage by your supplier’s bag weight (often about 0.8–0.85 tonnes). So 2 tonnes is roughly 2.5 bulk bags, meaning you’d order three. Don’t assume one bag equals one tonne, or you’ll be short.
Is it cheaper to buy gravel in bulk bags or loose?
Loose tipped delivery by the tonne is usually the cheapest per kilo for large jobs, followed by bulk bags, with small handy bags the most expensive. The best choice depends on how much you need and whether a lorry can tip loose material where you want it.
How much does a bulk bag of gravel weigh?
Typically around 800–850kg for standard 20mm gravel — about 0.8 tonnes and roughly 0.5 m³. Denser materials weigh more in the same bag, and half bulk bags of around 0.4 tonnes are also available from many suppliers.