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Garden Soil Calculator: How Much Soil Do I Need for My Raised Bed?

Calculate exactly how much soil you need for your garden bed, raised bed, or planter. Enter length, width, and depth — get volume in m³, litres, and number of bags, with the 15% settling allowance included. Free, accurate, no sign-up.

🗓️ Updated June 2026 Reviewed by Martín Rodríguez

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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed: Jun 20, 2026

Length of bed or planter*

Width of bed or planter*

Soil depth (usable layer only)*

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Getting the right amount of soil before heading to the garden centre saves money, time, and unnecessary return trips. This calculator uses the standard horticultural volume formula — length × width × depth — to tell you exactly how many cubic metres of soil or compost your garden bed needs, along with the litre equivalent and how many bags to buy.

Whether you are filling a new raised bed, topping up a planter on a balcony, or preparing a vegetable patch, the maths is the same: multiply the three dimensions of the space that needs to be filled. The result is your base volume. Most gardening authorities — from the USDA NRCS to the UK Royal Horticultural Society — recommend adding 10–15 % on top to account for natural settling after watering and compaction over the first growing season. This calculator applies the standard 15 % settling allowance automatically.

When to use this calculator

Planning a new vegetable patch — You want to build a raised bed 2.4 m long × 1.2 m wide × 0.35 m deep for tomatoes and lettuce. The calculator gives 2.4 × 1.2 × 0.35 = 1.008 m³ = 1,008 L. With the 15 % settling allowance: 1.16 m³ = 1,160 L — approximately 24 bags of 50 L or 15 bags of 80 L. Buying in bulk from a garden supply yard is typically 30–50 % cheaper for volumes over 0.5 m³.
Balcony planter with structural weight limits — Your balcony has a load rating of 200 kg/m² and you want a planter 1.5 m × 0.4 m × 0.3 m. Volume = 0.18 m³ = 180 L. Using heavy topsoil (≈1,000 kg/m³) would put 180 kg over 0.6 m² = 300 kg/m², exceeding the limit. Switching to lightweight perlite-based substrate (≈350 kg/m³) brings the load down to 63 kg over 0.6 m² = 105 kg/m², safely within the rating.
Urban rooftop garden with multiple planters — You are installing 6 raised beds, each 2 m × 0.8 m × 0.3 m, on a rooftop terrace. Each bed needs 0.48 m³ = 480 L; six beds total 2.88 m³ = 2,880 L. With 15 % settling: 3.31 m³. Ordering in bulk from a landscape supplier and specifying a lightweight growing media reduces both cost and structural load significantly.
School horticulture project — A school garden programme needs to fill 4 rectangular beds, each 3 m × 1 m × 0.3 m. Total volume: 4 × (3 × 1 × 0.3) = 3.6 m³ = 3,600 L. With settling allowance: 4.14 m³. The calculated figure is used to prepare a budget estimate and procurement order, with a concrete number that can be submitted for approval.

Recommended Soil Depth by Plant Type

Plant type	Minimum depth
Lawn and groundcover	15 cm
Herbs and leafy greens (lettuce, spinach)	20–25 cm
Root vegetables (carrots, beets)	30–40 cm
Fruiting vegetables (tomatoes, peppers)	35–45 cm
Shrubs and small fruit trees	45–60 cm

Fuente: Royal Horticultural Society — Soil and Compost (rhs.org.uk)

How it works

How to Calculate How Much Soil You Need

The soil volume formula is straightforward geometry:

Volume (m³) = Length (m) × Width (m) × Depth (m)

Example: a raised bed 2.4 m × 1.2 m × 0.35 m needs 2.4 × 1.2 × 0.35 = 1.008 m³ = 1,008 litres of soil.

Settling allowance (15 %)

The USDA NRCS and the Royal Horticultural Society both recommend ordering 10–15 % more soil than your calculated volume to compensate for natural settling after watering and compaction during the first growing season. This calculator applies a standard 15 % allowance:

Volume with settling = Calculated volume × 1.15

From m³ to litres and bags

1 m³ = 1,000 litres

Bags of 50 L: divide total litres (with settling) by 50, round up

Bags of 80 L: divide total litres by 80, round up

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Quick reference table: how much soil by bed size

Bed size	Depth	Volume	With 15%	50 L bags
1 m × 0.5 m	0.25 m	0.125 m³ (125 L)	0.144 m³ (144 L)	3 bags
2 m × 1 m	0.30 m	0.600 m³ (600 L)	0.690 m³ (690 L)	14 bags
2.4 m × 1.2 m	0.35 m	1.008 m³ (1,008 L)	1.159 m³ (1,159 L)	24 bags
3 m × 1.5 m	0.40 m	1.800 m³ (1,800 L)	2.070 m³ (2,070 L)	42 bags
4 m × 2 m	0.45 m	3.600 m³ (3,600 L)	4.140 m³ (4,140 L)	83 bags

> For volumes over 0.5 m³, buying in bulk from a garden or landscape supply yard is typically 30–50 % cheaper than bagged soil.

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For non-rectangular beds

Circular: V = π × radius² × depth — e.g. 1 m diameter × 0.3 m deep → V = 3.1416 × 0.25 × 0.3 = 0.236 m³

L-shaped or irregular: break into rectangles, calculate each separately, then add.

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Recommended soil depths by plant type

Crop type	Minimum depth
Lawn and groundcover	15 cm
Herbs and leafy greens (lettuce, spinach)	20–25 cm
Root vegetables (carrots, beets)	30–40 cm
Fruiting vegetables (tomatoes, peppers)	35–45 cm
Shrubs and small fruit trees	45–60 cm

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Soil types and approximate weight

Soil type	Best use	Weight (kg/m³)
Heavy topsoil	Ground-level beds, lawn	900–1,100
Topsoil + compost 60/40	Vegetable and herb beds	700–900
Bagged garden soil	Raised beds, containers	400–600
Lightweight substrate (perlite/coco)	Balconies, roof gardens	200–400

> Tip: For balconies and rooftops, always check the structural load rating of the surface. Heavy topsoil at 1,000 kg/m³ can easily exceed typical residential balcony ratings of 150–300 kg/m². Use lightweight substrate when in doubt.

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Common mistakes when calculating soil for a garden bed

1. Skipping the settling allowance: Freshly placed soil settles 10–20 % after the first few waterings. Buying exactly the calculated volume almost always leaves the bed short.
2. Measuring total container depth instead of usable depth: If your planter is 40 cm tall but has an 8 cm drainage layer at the bottom, the usable soil depth is only 32 cm. Enter 0.32 m, not 0.40 m.
3. Confusing litres and cubic metres: Bags are sold in litres. Remember: 1 m³ = 1,000 L. A 50 L bag is 0.05 m³.
4. Choosing the wrong soil type for the application: Heavy topsoil outdoors is fine; on a balcony it is a structural risk. Match soil weight to the rated load of the surface.

Raised vegetable bed: 2.4 m × 1.2 m × 0.35 m

Length: 2.4 m | Width: 1.2 m | Soil depth: 0.35 m

Volume = 2.4 × 1.2 × 0.35 = 1.008 m³ = 1,008 litres

With 15 % settling allowance: 1.159 m³ ≈ 1,159 L

Equivalent to: 24 bags of 50 L or 15 bags of 80 L

1.008

Frequently asked questions

How much soil do I need for a raised garden bed?

Multiply the interior length, width, and desired soil depth of your raised bed in metres: Volume (m³) = Length × Width × Depth. Then add 15 % for settling. Example: a 2 m × 1 m bed filled to 0.3 m deep needs 2 × 1 × 0.3 = 0.6 m³ = 600 litres. With settling: 0.69 m³ = 690 L — about 14 bags of 50 L. This calculator does it all automatically.

How deep should soil be in a raised garden bed?

It depends on what you are growing. Leafy greens and herbs need at least 20–25 cm; fruiting vegetables like tomatoes and peppers need 35–45 cm; root vegetables like carrots need 30–40 cm. For a general-purpose raised bed, 30 cm (0.3 m) is a common minimum that works for most crops.

Why do I need to add extra soil for settling?

Freshly placed soil is loose and full of air pockets. After the first few waterings, those gaps compress and the volume shrinks by 10–20 %, depending on the soil type. Compost-heavy mixes settle more; sandy mixes settle less. Adding 15 % to your order means the bed stays at the right depth through the first growing season.

How many bags of soil do I need for my garden bed?

Calculate the volume in litres first: Volume (m³) × 1,000 = litres. Then add 15 % for settling and divide by the bag size. Example: 0.6 m³ × 1.15 × 1,000 = 690 L. Divide by 50 (bag size in litres) = 13.8 → buy 14 bags of 50 L. Divide by 80 = 8.6 → buy 9 bags of 80 L. Always round up.

What is the difference between topsoil, garden soil, and potting mix?

Topsoil is raw mineral soil used mainly for filling and levelling — low in organic matter. Garden soil is topsoil enriched with compost and nutrients, designed for beds and borders. Potting mix (or potting compost) is a lightweight, peat- or coco-based blend formulated for containers and raised beds where drainage and weight matter. This calculator gives you the volume; choose the type based on your planting needs.

Should I buy soil in bags or in bulk?

For under 0.5 m³ (500 L), bags are usually more practical — no delivery minimum and you can mix types. Above 0.5 m³, buying in bulk from a garden or landscape supply yard is typically 30–50 % cheaper per cubic metre, even after delivery. Ask for 'screened topsoil' or 'garden-grade compost' to ensure quality and avoid debris.

How do I measure an L-shaped or irregular garden bed?

Split the area into simpler rectangles. Calculate the volume of each rectangle (length × width × depth) and add them together. For beds with an uneven base, use the average depth: (minimum depth + maximum depth) ÷ 2. This method gives a reliable estimate for most irregular shapes.

Can I use this calculator for circular or round planters?

This calculator handles rectangular beds. For circular planters, use: Volume = π × radius² × depth. For example, a round planter 0.8 m in diameter (radius = 0.4 m) and 0.25 m deep needs 3.1416 × 0.16 × 0.25 = 0.126 m³ = 126 L. Add 15 % for settling: about 145 L.

Does the drainage layer at the bottom of a planter count as soil depth?

No — it should not be counted. If your planter is 40 cm tall but you place an 8 cm gravel drainage layer at the bottom, enter 0.32 m as the depth (not 0.40 m), since plants root into the soil layer, not the gravel. Measuring the total container depth instead of the usable soil depth is one of the most common reasons people over-buy soil.

How heavy will my raised bed be once filled with soil?

Multiply the soil volume (m³) by the bulk density of the soil type. Wet topsoil weighs about 1,000–1,100 kg/m³; bagged garden soil 400–600 kg/m³; lightweight perlite-based substrate 200–400 kg/m³. For example, a 0.6 m³ raised bed filled with wet topsoil can weigh up to 660 kg. On balconies and rooftops, always check the structural load rating before choosing soil type.

What compost ratio should I mix with topsoil?

Most gardening authorities recommend a 60/40 mix of topsoil to compost for vegetable beds and herb gardens. For a 1 m³ total volume, that means roughly 0.6 m³ of topsoil and 0.4 m³ of compost. Compost-heavy mixes settle more (up to 20 % in the first year), so increase your settling allowance to 20 % when using high-compost blends.

Is this soil volume formula used by professional landscapers?

Yes. Volume = Length × Width × Depth is the standard formula used in horticulture, landscaping, and civil engineering for rectangular soil volumes. Professional estimates typically add a compaction or waste factor of 10–20 %, equivalent to the 15 % settling allowance this calculator applies. The USDA NRCS and leading horticulture references all use the same base formula.

Sources & references

Methodology & trust

Editorial

Calculadora de construcción revisada por el equipo editorial de Hacé Cuentas, contrastada con USDA Natural Resources Conservation Service — Soil Health, según nuestra política editorial y metodología.

Updates

Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). Garden Soil Calculator: How Much Soil Do I Need for My Raised Bed?. Hacé Cuentas. https://hacecuentas.com/garden-soil-volume-calculator

Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.

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