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How to fill a raised bed

Updated: October 2026

The frame is on the lawn, or the bags are still in the boot, and you need to know how to fill a raised bed before you plant. The figure that matters is the soil in the growing wall. Measure its length, width and depth, then buy a mix that is mostly topsoil. This page covers the litre sum, the Royal Horticultural Society ratio, cardboard on grass, and a slow fill that keeps thin sides straight. If you are still choosing the frame, start with the [raised bed comparison](/hub/raised-beds-greenhouses-and-compost/raised-bed), where the stated volume sits beside each kit. The Products Compared editorial team updated this guide on 16 October 2026 from those listing figures and from public RHS advice. A purchase through a link on the comparison can earn us a commission at no extra cost to you.

The frame is on the lawn, or the bags are still in the boot, and you need to know how to fill a raised bed before you plant. The figure that matters is the soil in the growing wall.

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Harbour Housewares Harbour Housewares raised beds, pack of 2

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Ergohortus Ergohortus oval raised beds, 2-pack

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Ergohortus Ergohortus oval raised beds, 2-pack
8.3/10about £38.99
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VIREO GARDEN VIREO GARDEN round raised bed, 2-pack

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VIREO GARDEN VIREO GARDEN round raised bed, 2-pack
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On this page
  1. 1.Litres from the soil wall
  2. 2.What the RHS puts in the bed
  3. 3.Cardboard, film and braces before the soil
  4. 4.After the level drops

Litres from the soil wall

Multiply length by width by soil depth, in metres, then multiply by 1,000 to get litres. A wall of 180 cm by 90 cm by 30 cm is 1.8 × 0.9 × 0.3, which is 0.486 cubic metres, or 486 litres. As a rule of thumb that is about ten 50-litre bags before the mix settles. A larger bed takes more once bulky waste goes in the base. Depth changes the bag count more than a slightly longer side. The raised bed buying guide is where you settle that depth if the frame is not built yet.

What the RHS puts in the bed

On soil, the RHS fill is seven parts topsoil, three parts organic matter and two parts sharp sand. Topsoil is the bulk, the organic matter feeds the bed, and the sharp sand helps it drain. Compost belongs in the organic share. Used alone, it slumps, and you top the bed up the next season. Ask for peat-free compost in that share, beside the topsoil. If the ticket is silent, check before you accept the load. Sandwich Handyman says to ask whether the topsoil meets BS 3882, the British standard. Use only the name on the delivery note. On a hard surface the RHS fill uses four parts sand, and patio drainage is on raised bed on concrete.
Harbour Housewares Harbour Housewares raised beds, pack of 2

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Harbour Housewares Harbour Housewares raised beds, pack of 2
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Cardboard, film and braces before the soil

On grass, lay overlapping cardboard, wet it, and run it to the inner face so couch grass has no gap. It rots, and worms can pass. A plastic sheet across the floor holds water, so leave the base open to the soil. Thin metal bows if the soil goes in as one tip. FOUBAM buyers describe bowed panels after a fast fill. Peel the film and fit the rods or braces while the bed is empty, then fill in layers and firm each layer from the middle. Finish a little below the rim so the first watering stays inside the wall. Zinc, rot and edge heat are set out on galvanised raised bed vs timber. Call a landscaper when the work is breaking ground, walking a bulk bag through the house, or setting the bed on a deck. Wet soil is heavy, and a domestic barrow is a poor tool for a tonne bag.

After the level drops

Organic matter shrinks, and a bed filled to the rim can sit several centimetres lower by spring. Top up with the same mix. A thick compost cap slumps again, though a thin mulch on a topsoil body is a smaller job. Cardboard, as with about 150 litres against the Ergohortus stated 216, cuts the first fill and still leaves a later top-up. If a side bows after rain, take some soil out, refit the brace and refill in layers.

Common questions

How many litres is a 180 x 90 x 30 cm raised bed?
A soil wall of 180 × 90 × 30 cm holds 486 litres, from 1.8 × 0.9 × 0.3 metres. That is about ten 50-litre bags before settlement and before cardboard in the base. The 2,916 litre KING BIRD figure runs up to the trellis. Order from the soil depth, and keep a little aside for the first season's drop.
What mix does the RHS publish for a raised bed?
On soil the RHS uses seven parts topsoil, three parts organic matter and two parts sharp sand. Peat-free compost can be the organic part. On a hard surface the guidance uses four parts sand. Equal parts topsoil, compost and manure is a workshop mix with a different balance. Leave the surface a little below the rim.
Can you fill a raised bed with compost only?
Compost on its own slumps as it rots, and it costs more per litre than topsoil. The level is then hard to keep even. Keep compost to the organic share beside topsoil. A thin mulch on a finished topsoil mix is reasonable if you renew it when it disappears.
Should you put plastic under a raised bed?
On soil or grass, leave the floor open. Overlapping cardboard suppresses turf, then rots, and water can pass. A plastic sheet across the base holds water in the lower layer. Peel film off the metal panels before you fill. Paving needs a separate drainage plan.
Does a raised bed need topping up after it settles?
Most beds drop several centimetres in the first season as the organic matter shrinks. Top up with the same mix, and keep the surface below the rim. The soil also dries faster than the ground beside it, so a water butt nearby is worth having. You still need to water in a dry week.
When should you order a bulk bag?
Past a few hundred litres, a bulk bag is easier than a boot full of 50-litre sacks, if the lorry can get close. Ask for topsoil to BS 3882 and for peat-free compost. If the bag must come through the house, or you are levelling a slope, a landscaper should do that part. Check a deck before any soil arrives.

Related pages

Best raised garden bed

Raised bed

Raised bed buying guide: depth, width and fill cost

Galvanised raised bed vs timber for a wet UK winter

Raised bed on concrete or paving: depth and drainage

Sources

Public UK sources from the research digest, last checked on 16 October 2026.

  1. RHS — How to make a raised bed (retrieved 16.10.2026)
  2. RHS — Growing veg in raised beds (retrieved 16.10.2026)
  3. RHS — No-dig gardening (retrieved 16.10.2026)
  4. RHS — Creating raised beds for schools (retrieved 16.10.2026)
  5. Thrive — Wheelchair-friendly garden design (retrieved 16.10.2026)
  6. GOV.UK — Permitted development technical guidance (retrieved 16.10.2026)
  7. legislation.gov.uk — Consumer Rights Act 2015 (retrieved 16.10.2026)
  8. Quickcrop — Timber raised beds vs metal raised beds (retrieved 16.10.2026)