Soil is best planned by volume
Topsoil fills a space, so cubic volume is the primary quantity. Weight is much less predictable because moisture, mineral content and organic matter vary. AmountHub therefore keeps volume prominent and uses density only as an approximate secondary check.
Worked example
A 6 m × 3 m bed with 10 cm of new soil needs 1.8 m³ before allowance. Adding 5% gives about 1.89 m³. At 1.30 t/m³ that is approximately 2.46 tonnes, or 48 bags when using 40-litre bags.
Use the supplier’s bulk density when available
Volume and bag count come from the bed dimensions and labelled bag size. Weight is a secondary delivery estimate. Choose “Use supplier density” if a specific product is quoted by weight. In the 1.89 m³ worked example, entering 1.50 t/m³ changes the approximate weight to 2.84 tonnes while leaving the 48 × 40-litre bag estimate unchanged. In Imperial mode, enter density in lb/yd³.
Settling should be a separate decision
Fresh soil often consolidates after watering and rainfall. Rather than hiding extra settling inside the basic geometry, the planning panel lets you add a separate reserve. That makes it clearer which quantity comes from measurement and which part is a judgement about site conditions.
Different projects need different depths
| Project | What to measure | Planning note |
|---|---|---|
| Lawn top-dressing | Lawn area × added depth | Do not use full root-zone depth. |
| New garden bed | Bed area × new soil depth | Allow for settlement where appropriate. |
| Raised bed | Inside dimensions × fill depth | Subtract existing fill. |
| Levelling | Area × average fill depth | Take several depth readings. |
How bag units work
Enter the product volume printed on the bag: litres in Metric mode or cubic feet in Imperial mode. Switching units converts the quantity already entered. A 40-litre bag is about 1.41 ft³. Bag count uses volume, whereas the approximate transport weight uses density.
Bagged versus bulk soil
Bags are convenient for small or awkward-access projects; bulk delivery becomes more practical as volume increases. The planning options round bulk volume to a supplier increment while also showing the number of bags at the package size you entered.
Before ordering soil
- Measure the depth you are actually adding, not the final total soil profile.
- Check whether the product is suitable for turf, vegetables or ornamental planting.
- Use inside dimensions for raised beds.
- Allow for settlement deliberately rather than automatically.
- Keep finished levels clear of trunks, stems, walls and drainage details.
Calculate only the new fill
A raised bed that is 2 m by 1 m and already contains 20 cm of usable fill may need only another 10 cm. The added volume is 2 × 1 × 0.10 = 0.20 m³, or 200 litres before an allowance. Entering the entire 30 cm depth would triple that estimate. For uneven ground, measure the fill depth in several spots and use a reasoned average, or divide the bed into sections.
Frequently asked questions
Does soil weight tell me how many bags to buy?
Use volume and the bag's labelled litres for the bag count. The weight is an approximate transport check because damp and dry topsoil differ substantially.
Is the extra allowance the same as the settling reserve?
No. The main allowance is part of the initial estimate; the optional planning reserve adds more for expected consolidation. Avoid adding both automatically without considering site conditions.
Can I use this for potting mix?
The volume and bag calculation still work, but the topsoil weight assumptions are unsuitable for many lightweight potting mixes. Choose bag volume and ignore the approximate weight.