Raised Bed Calculator — How Much Soil to Fill a Raised Garden Bed
Raised beds need a lot more soil than most people expect. A 1.2 m × 2.4 m bed that is 300 mm deep holds over 860 litres. This calculator converts your bed dimensions to litres, then tells you how many bags to buy — no surprises at the checkout.
How we calculate
Volume = length × width × depth (m). Litres = volume × 1000. Bags = ⌈litres ÷ bag volume⌉.
Worked example
2.4 m × 1.2 m × 300 mm: 2.4 × 1.2 × 0.3 = 0.864 m³ = 864 L. At 50 L/bag: ⌈864 ÷ 50⌉ = 18 bags.
Common mistakes
- Filling entirely with compost — pure compost compacts and becomes waterlogged; blend with topsoil and perlite.
- Underestimating how much the soil will settle — fill the bed to the brim, as it can settle 20–30% in the first season.
- Not lining the bottom — hardware cloth or cardboard keeps out burrowing pests and suppresses weeds from below.
- Using garden soil directly — it compacts heavily in a raised bed and drains poorly without added structure.
Frequently asked questions
How much soil do I need to fill a raised bed?+
A standard 2.4 m × 1.2 m bed at 300 mm deep holds 864 litres — about 18 bags at 50 L each. Raised beds hold far more than most people expect. Use this calculator to get the exact bag count for your dimensions before heading to the garden centre.
What is the best soil mix for a raised bed?+
A good all-round mix is roughly one-third topsoil, one-third compost, and one-third perlite or coarse grit. Pure compost collapses and waterlogged; topsoil alone compacts. The blend gives good drainage, nutrients, and structure.
How deep does a raised bed need to be for vegetables?+
Most vegetables need at least 300 mm. Shallow-rooted crops like lettuce and herbs do fine at 150 mm. Root vegetables (carrots, parsnips) benefit from 450 mm or more. Deeper beds also dry out more slowly in summer.
Does raised bed soil settle after filling?+
Yes — expect 20–30% settlement in the first growing season as the mix compacts and organic matter breaks down. Fill the bed right to the top when planting, and plan to top up with compost each spring to maintain the level.