How to Build a Raised Bed: Materials, Costs and Filling Guide

Quick answer: A standard raised bed is built from timber, sleepers, or composite boards, sits 20–40cm high, and is typically 1.2m wide so it can be reached from both sides without stepping into the bed. For a 2m × 1m bed at 20cm deep, budget for around 400 litres of fill — ideally a 50/50 blend of topsoil and compost — plus the cost of the frame material itself. Most first-time raised bed builders underestimate the fill volume far more than the construction cost, so it's worth calculating both before ordering materials.

Building a raised bed is a two-part project — the frame, and what goes inside it — and most guides only cover one or the other. This one covers both: how to size and build the frame itself, then exactly how much material to order to fill it properly, so you're not caught out by a delivery that's too small (or too large) once the bed is built.

What size should a raised bed be?

A width of 1.2m or less is the key rule for raised bed sizing, since it allows the centre of the bed to be reached from either side without stepping onto the soil and compacting it — length can vary based on space, but 1.8–2.4m is typical for a manageable single bed. For depth, 20–30cm suits most vegetables, while 15cm is enough for shallow-rooting salad crops and 40cm+ benefits deep-rooting crops like carrots or if the bed sits on a hard surface like a patio with no soil access underneath.

What materials should I build a raised bed frame from?

Timber, sleepers, and composite boards are the most common raised bed materials, each with a different balance of cost, appearance and lifespan.

Avoid old, reclaimed railway sleepers for vegetable beds specifically — older sleepers were often treated with creosote, which isn't suitable for growing edible crops. New, untreated or appropriately treated sleepers sold for garden use are the safer choice.

How do I calculate how much soil and compost to fill a raised bed?

Use the standard volume formula: length (m) × width (m) × depth (m) = volume in cubic metres, multiplied by 1,000 for litres. For a 2m × 1m bed filled 20cm (0.2m) deep:

2 × 1 × 0.2 = 0.4m³ = 400 litres

Add 10–15% on top of the raw calculation to account for settling once the bed has been watered and had time to bed in — a bed that looks perfectly full on day one often needs a top-up within a few weeks.

What should I fill a raised bed with?

A 50/50 blend of topsoil and compost is the standard fill for most raised beds — topsoil provides the structural bulk and body, while compost adds the organic matter and nutrients plants need, and the combination settles less over time than pure compost on its own. For very deep beds, some growers use a cheaper bulk fill (subsoil, coarse organic matter, or even upturned turf) in the bottom third, with the topsoil/compost blend reserved for the top 20–30cm where roots are most active.

This "lasagne" or layered approach reduces the amount of premium topsoil and compost needed for very deep beds, since the bulk of the depth is filled with cheaper or free material before the growing layers go on top.

How much does it cost to build and fill a raised bed?

Costs vary by material and size, but as a rough guide for a standard 2.4m × 1.2m bed at 25cm depth: timber or sleeper frame materials typically run from moderate for basic timber to significantly more for sleepers or composite boards, while the fill (roughly 720 litres, just under one bulk bag) is usually a smaller portion of the total cost than most first-time builders expect. Ordering fill material in bulk rather than multiple small bags brings the per-litre cost down considerably, particularly once a project needs more than 2–3 standard garden centre bags.

Should I put anything down before filling a raised bed?

If the bed sits on grass or existing soil, laying cardboard or weed-suppressant membrane on the ground first helps prevent weeds and grass growing up into the new bed, though this is optional if the bed is deep enough (30cm+) that weeds are unlikely to be a significant problem. If the bed sits on a hard surface like a patio or decking, drainage becomes more important — ensure there's adequate depth and consider a coarser material at the base to prevent waterlogging, since there's no natural soil below to draw excess water away.

Is Kelvin topsoil and compost suitable for filling raised beds?

Yes. Our ready-blended Topsoil Compost Mix is designed specifically for filling raised beds in one product, avoiding the need to order and mix topsoil and compost separately. It's produced at our site in Chapelton, South Lanarkshire, to the BSI PAS 100 standard, with no synthetic chemicals or peat.

Ordering raised bed fill in Glasgow

1. Build or measure your bed frame first, so you have exact internal dimensions
2. Calculate your fill volume using the formula and tables above
3. Order Topsoil Compost Mix, or separate Top Soil and Organic Compost, through our product pages, or call +44 7561 251350 for larger multi-bed orders

We deliver across Glasgow, East Kilbride and South Lanarkshire (£15 local delivery in East Kilbride and surrounding areas), with quotes available for the wider Central Belt.

Frequently Asked Questions

How wide should a raised bed be? No wider than 1.2m if it will be accessed from both sides, so the centre can be reached without stepping into the bed and compacting the soil. Beds against a wall, accessed from one side only, should be no more than 60cm wide.

Can I use just compost to fill a raised bed? You can, but it's not usually the best choice — pure compost is more expensive to fill a bed with than a topsoil blend, holds more moisture than most vegetables want long-term, and settles more over a season than a soil-based mix.

How deep does a raised bed need to be for vegetables? Most vegetables do well with 20–30cm of depth. Deep-rooting crops like carrots and potatoes benefit from 30–40cm, while shallow crops like salad leaves and herbs can manage with as little as 15cm.

What's the cheapest way to fill a large raised bed? For very deep beds, filling the bottom third with cheaper bulk material (coarse organic matter, subsoil, or woody prunings) before adding the topsoil and compost blend on top reduces the amount of premium fill material needed.

Do I need to line a raised bed made of timber? Lining isn't essential, but a plastic liner between the timber and the soil can extend the frame's lifespan by reducing direct contact with damp soil, particularly for untreated or lower-grade timber.