Gardeners Toolkit
Free raised-bed volume calculator

Raised Bed Soil Calculator

Calculate the volume you still need to fill using the bed's internal dimensions, your chosen finished depth and any material already inside.

Internal dimensionsExisting fillMultiple beds
Raised bed cross section showing internal measurements, existing fill and remaining soil depthinside lengthtotal fillnew materialalready in bed

Calculate the empty space you actually plan to fill

Raised beds are best measured on the inside. If the bed already contains soil, rubble, inverted turf or another deliberate lower fill, subtract its depth rather than ordering for the full frame height.

Deep bed?

The calculator tells you the volume you choose to fill. It does not assume a deep structure must be filled top-to-bottom with premium topsoil or compost.

Calculate raised-bed fill

Use internal dimensions and set the final fill depth separately from material already in the bed.

Filling help
Step 1

Measure the bed inside the frame

Step 2

Set the fill depths

Enter 0 for an empty bed.
L
%

Your raised-bed estimate

Total fresh material—

— litres across — bed(s), using a remaining fill depth of —.

Volume per bed—
Whole bags — base—
Whole bags — order—
The calculator does not choose your soil recipe

It calculates volume only. Your material mix depends on crops, drainage, existing soil, bed depth and the products you use.

Plan the fill, not just the volume

How should the bed be filled?Work through base conditions, depth, soil structure, settlement and material choices.Buying topsoil separately?Calculate the soil component using supplier pack information.Adding organic matter?Calculate compost separately rather than assuming a universal mix ratio.Actually a freestanding planter?Use container geometry if the project is closer to a pot than an open-bottom bed.

Internal size and chosen fill depth are the important measurements

A 2m × 1m bed filled to 300mm needs 0.6m³, or 600 litres. If a 600mm-deep structure already contains 200mm of deliberate lower fill and you only need the upper 400mm, use 400mm as the fresh-material depth rather than ordering for the full frame.

measure inside the frameUse internal dimensionsTimber, masonry or metal walls do not hold soil, so external dimensions overstate the fill volume.
fresh fillexisting fillSubtract existing materialOnly calculate the empty depth you intend to fill with new material.

Deep raised beds do not have one universal fill method

Current RHS guidance says bed size and depth depend on what you plan to grow. For beds deeper than 50cm, its raised-bed guide describes using lower-value materials such as rubble or subsoil in the base to improve drainage and reduce the quantity of good soil needed, then finishing with a suitable growing layer. The same guide recommends leaving filled beds to settle and topping up if necessary.

About soil and compost mixes

There is no reason for this calculator to force every gardener into a 50/50, 60/40 or 70/30 recipe. RHS publishes a general raised-bed mixture for many situations, but also changes that advice for plants requiring greater drainage and for beds on hard surfaces. That is exactly why the calculator keeps volume separate from horticultural material choice.

Source note

RHS raised-bed guidance currently gives a general mixture of topsoil, organic matter and sharp sand for many beds, while explicitly varying the proportions for different drainage needs and construction conditions. Use the linked guide for context rather than assuming a universal ratio.

Common mistakes

  1. Measuring the outside of the bed instead of the planting space.
  2. Ordering for the full frame height when some lower fill already exists.
  3. Assuming every bed needs the same soil/compost ratio.
  4. Forgetting that freshly filled material can settle after watering and time.
  5. Buying only small bags before comparing whether loose or bulk supply is practical for a large volume.
Check the depth & volume referenceVerify litres per square metre and area × depth conversions.