Tonnes vs Bulk Bags: How to Convert Aggregates and Work Out What to Order
Aggregates are measured in a confusing mix of units. Your plan is in square metres and millimetres, the quarry thinks in cubic metres, you order in tonnes, and the delivery arrives in bags. This guide shows how to convert between them, so you order the right amount first time.
The units
- Cubic metre (m³): volume. This is what you get from length × width × depth.
- Tonne: weight, 1,000kg. This is how aggregates are usually priced and discussed.
- Bulk bag: a large single bag. Ours are approximately 800kg each, and the packed weight can be up to 850kg depending on moisture.
- Trade pack: a smaller bag, approximately 20 to 25kg, which varies with moisture.
Cubic metres to tonnes
To go from volume to weight, you need a density. These are typical loose densities, which vary by quarry and moisture:
| Material | Rough loose weight per m³ |
|---|---|
| MOT Type 1 and hardcore | About 1.7 tonnes |
| Sharp sand, building sand | About 1.6 tonnes |
| Gravel and shingle | About 1.6 tonnes |
| All-in ballast | About 1.7 tonnes |
Then tonnes = volume to order × density. For stone that will be compacted, add an allowance of 20 to 30% to the volume first. Once compacted, MOT Type 1 weighs more per m³ than it does loose, and about 2.1 to 2.2 tonnes per finished m³ is commonly quoted. Our 25% allowance on the loose weight gives about 2.1, so the two methods agree.
Tonnes to bulk bags
Divide by 0.8 and round up:
- 0.8 tonnes is 1 bag
- 1 tonne is 1.25 bags, so order 2 for 1 tonne
- 2.55 tonnes is 3.2 bags, so order 4
- 5 tonnes is 6.25 bags, so order 7
Bags are sold whole, so you pay for the rounding. If you are just over a whole number, it is worth thinking about whether the extra is useful, for example for topping up a path, or whether a few 25kg bags would cover the difference.
Tonnes to 25kg bags
Forty 25kg bags make a tonne. Our trade packs are approximately 20 to 25kg, so allow a few more if you are working to a tight figure. They are handy for small jobs and top-ups, for carrying through a house, and anywhere a bulk bag will not fit.
How big is a bulk bag?
An 800kg bag of material at 1.7 tonnes per m³ is about 0.47m³, and of sand at 1.6 tonnes per m³ about 0.5m³. So roughly half a cubic metre of loose material per bag, which is a handy check when you compare quotes given in cubic metres.
Bulk bags or small bags: what costs less?
At the time of writing, our bulk bags are £48.75 ex VAT for sharp sand, MOT Type 1 and the gravels, and our trade packs are £2.25 ex VAT.
- A bulk bag works out at about £61 ex VAT per tonne (£48.75 ÷ 0.8).
- Trade packs, if each is a full 25kg, work out at about £90 ex VAT per tonne (40 × £2.25).
So bulk bags are the better value for anything bigger than a small job, and trade packs earn their keep for convenience. Bag weights are approximate, so treat these as a guide.
Worked example: converting a patio
- 4m × 3m patio at 100mm deep: area 12m², finished volume 1.2m³.
- With a 25% allowance for compaction: 1.5m³ to order.
- At 1.7 tonnes per m³: about 2.55 tonnes.
- At 0.8 tonnes per bag: 3.2, so 4 bags of MOT Type 1.
The full working is in our guide to how much MOT Type 1 you need for a patio.
Picking the order up or having it delivered
Bulk bags are heavy, so you need to be ready for them. They are lifted from the lorry with a truck-mounted forklift. Choose a firm, level spot the driver can reach safely, and have someone there to receive the delivery. Do not try to move a full bag by hand; plan to shovel from it where it is set down.
Frequently asked questions
How many 25kg bags make a tonne?
Forty, if each is a full 25kg. Our trade packs are approximately 20 to 25kg, so allow a few extra.
Why does a bulk bag weigh "approximately" 800kg?
Aggregates hold water, and a bag packed on a wet day weighs more than one packed in dry weather. Ours are approximately 800kg and can be up to 850kg.
Are cubic metres and tonnes interchangeable?
No. One cubic metre of sand weighs very roughly 1.6 tonnes, so you cannot swap one for the other without a density.
Is a tonne bag the same as a bulk bag?
Not here. Our bulk bags are approximately 800kg, which is slightly under a tonne.
How much extra should I order?
Allow 20 to 30% for compacted sub-base and about 10% for sand and gravel, then round up to whole bags.
Ordering and delivery
You can browse the full range in our cement and aggregates collection. Bulk bags are sold at approximately 800kg each (the packed weight can be up to 850kg depending on moisture), and most sands and gravels are also available in 20 to 25kg trade packs for small jobs. Prices on our website are shown excluding VAT, and VAT is added at checkout.
We deliver to addresses in mainland England only; we do not currently deliver to Wales, Scotland, Northern Ireland or the islands. Timber, aggregates and cement have a minimum order of £250 ex VAT, and delivery is £25 ex VAT on orders under £500 ex VAT and free over £500 ex VAT. Bulk bags are delivered by Moffett lorry (truck-mounted forklift) and offloaded at your site, so someone must be there to receive them and you will need a firm, level area with suitable access. We do not offer next-day delivery. Our shipping policy has the full details, or call us on 03330 908479 or email sales@insulationwarehousedirect.co.uk if you would like a hand working out your order.
The quantities in this guide are estimates. Ground levels, how well the material is compacted and how wet it is all change what you need, and densities vary between quarries, so check the amount with your installer or the manufacturer's guidance before you order. Prices and pack sizes are correct at the time of writing.