Raised Bed Soil Calculator

Calculate how much soil fills a raised garden bed in cubic feet, cubic yards and bags, with the compost, peat and vermiculite breakdown for a square foot garden mix.

By CalcBuilt Editorial TeamUpdated September 11, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To find how much soil a raised bed needs, multiply length by width by depth in feet for cubic feet, then divide by 27 for cubic yards or by the bag size for bags. An 8 x 4 ft bed 12 in deep holds 32 cubic feet, or 1.19 cubic yards, which is 22 bags of 1.5 cu ft, or about 10.7 cu ft each of compost, peat and vermiculite.

Results

Total soil: 1.19 cu yd; 32 cu ft to fill to the rim; fresh mix drops 10 to 20% the first season, so buy 15% over
Bags to buy: 22 bags of 1.5 cu ft; Or 16 bags of 2 cu ft. Past about 1 cu yd a bulk delivery is half the price per yard even with the delivery fee
Compost (1/3): 10.7 cu ft; Blend several kinds; bagged compost is usually 1 cu ft
Peat moss or coco coir (1/3): 10.7 cu ft; A 3 cu ft compressed peat bale loosens to about 6 cu ft
Coarse vermiculite (1/3): 10.7 cu ft; Sold in 4 cu ft bags at garden and hydroponic suppliers
Approximate weight: 1,920 lb; At about 60 lb per cubic foot, moist

Raised Bed Soil formula

Cubic feet = Length (ft) x Width (ft) x Depth (in) / 12 x number of beds
Cubic yards = Cubic feet / 27;  Bags = Cubic feet / bag size (1.5 or 2 cu ft)
Each component = Cubic feet x its share of the mix (1/3, 1/2 or all)
Weight (lb) = Cubic feet x 60

Worked example

Three 4 x 10 ft beds filled 18 in deep: 4 x 10 x 1.5 = 60 cubic feet each, or 180 cubic feet in all. 180 / 27 = 6.67 cubic yards. In bags that is 180 / 1.5 = 120 bags of 1.5 cu ft, or 90 bags of 2 cu ft, so a bulk delivery of 7 yards makes more sense.

With the half topsoil, half compost mix, that is 90 cubic feet (3.33 yards) of topsoil and 90 cubic feet of compost. At 60 lb per cubic foot the beds hold 180 x 60 = 10,800 lb, or 5.4 tons of soil.

Quick reference

Soil for common raised bed sizes
Bed size	10 in deep	12 in deep	18 in deep	1.5 cu ft bags at 12 in
2 x 4 ft	6.7 cu ft	8 cu ft	12 cu ft	6
2 x 8 ft	13.3 cu ft	16 cu ft	24 cu ft	11
3 x 6 ft	15 cu ft	18 cu ft	27 cu ft	12
4 x 4 ft	13.3 cu ft	16 cu ft	24 cu ft	11
4 x 6 ft	20 cu ft	24 cu ft	36 cu ft	16
4 x 8 ft	26.7 cu ft	32 cu ft	48 cu ft	22
4 x 12 ft	40 cu ft	48 cu ft	72 cu ft	32

How to calculate raised bed soil

Measure the inside of the bed, not the outside of the boards, and multiply length by width by the depth you plan to fill, all in feet. A 4 by 8 foot bed with 12 inches of soil is 4 x 8 x 1 = 32 cubic feet. Divide by 27 for cubic yards if you are ordering bulk, or by 1.5 or 2 for the number of bags.

Bags are convenient for one or two beds. A 1.5 cu ft bag of raised bed mix is typically $8 to $12 in 2026, which is $145 to $215 a yard. A landscape yard sells a topsoil and compost garden blend for typically $40 to $80 a yard. The delivery fee, typically $50 to $100, is the same for 1 yard as for 5, and most yards will not deliver under 1 yard. Past about a yard, order bulk and pick the drop spot first.

Choosing a mix

The square foot garden mix of equal parts compost, peat or coir, and coarse vermiculite is light, drains well and holds moisture. Vermiculite is the expensive part. A 4 cu ft bag is typically $40 to $60 in 2026, and a 4 x 8 ft bed at 12 in takes about 3 bags. For big beds, half screened topsoil and half compost is far cheaper and grows most vegetables well. Peat is acidic, so add a cup of garden lime per 3 cu ft bale. Never use plain topsoil or soil dug from the yard alone; it compacts and drains poorly in a box.

Fill beds to the rim and water well. The mix will drop an inch or two as it settles, and that is the space you top up with an inch of compost every spring. On lawn or soil, lay cardboard first to smother grass, or 1/2 in hardware cloth where gophers dig. On concrete or a patio, skip the gravel layer at the bottom; it perches water above itself instead of draining. Make the bed 18 to 24 in deep and leave weep gaps at the base of the boards.

What this calculator leaves out

The result is soil only. A 4 x 8 ft bed 12 in deep takes three 8 ft 2x12s, two for the sides and one cut in half. Add four 4x4 corner posts and 3 in exterior structural screws. Lumber treated since 2004 with ACQ, CA or MCA is copper based and fine for food beds; cedar lasts 10 to 15 years, untreated pine 3 to 5. Not included: cardboard or hardware cloth, drip line, mulch, the delivery fee, and the yearly compost top-up.

Mistakes that cost money

Gravel in the bottom for drainage perches the water table above it and keeps the mix soggy; leave the bottom open on soil.
Plastic sheet under the bed: no drainage and rotted roots. Use cardboard on lawn, or 1/2 in hardware cloth where gophers dig.
Salvaged pre-2004 CCA lumber or creosote railroad ties in a food bed; use ACQ or MCA treated, cedar, or redwood instead.
Planting the day the bed is filled: the mix drops 2 to 3 in the first month. Let it settle, top up, then plant.
A 4 x 8 bed at 12 in weighs 2,000 lb, or 60 psf; decks are designed for 40 psf (IRC R301.5). Build on grade.
8 ft 2x12 sides with no center stake bow 1 to 2 in the first season; add a cross tie or mid-span stake.

Key facts

Mel Bartholomew's square foot gardening mix is 1/3 compost, 1/3 peat moss and 1/3 coarse vermiculite by volume.
One cubic yard is 27 cubic feet, enough to fill a 4 x 8 ft bed 10 in deep (26.7 cu ft).
Bagged garden soil comes in 1.5 and 2 cu ft bags; a 40 lb bag of topsoil is only about 0.75 cu ft.
Most vegetables need 10 to 12 in of soil; carrots, parsnips and potatoes do better with 18 in.
Fresh mix settles 10 to 20 percent in the first season, so fill beds to the rim and top up with compost each spring.
Lumber treated since 2004 (ACQ, CA, MCA) is copper based and accepted by extension services for food beds; CCA was withdrawn from residential use in 2003.

Frequently asked questions

How much soil do I need for a 4x8 raised bed?

32 cubic feet, or 1.19 cubic yards, at 12 in deep. That is 22 bags of 1.5 cu ft or 16 bags of 2 cu ft. At 10 in deep it takes 26.7 cubic feet, just under one yard.

Is pressure-treated lumber safe for a vegetable bed?

Lumber treated since 2004 is. The EPA withdrew arsenic-based CCA from residential lumber at the end of 2003. Today's ACQ, CA and MCA treatments are copper based, and extension trials find the copper stays within an inch of the wood. Use ground-contact (UC4A) boards, and if you want a barrier, staple 6 mil poly to the sides only, never the bottom. Skip salvaged CCA and creosote ties.

What is the best soil mix for a raised bed?

Equal parts compost, peat moss or coco coir, and coarse vermiculite is the classic square foot gardening mix. For large beds, half screened topsoil and half compost is cheaper and works well.

How deep should a raised bed be?

10 to 12 in of soil is enough for most vegetables and herbs. Root crops and beds on concrete or compacted ground should be 18 in deep.

Sources and references

Raised bed gardens (bed depth, soil mixes and filling) (University of Minnesota Extension)
Soil to Fill Raised Beds (compost and topsoil ratios, 8 to 24 in depth) (University of Maryland Extension)
Raised Bed Gardening (1:1:1 compost, drainage material and topsoil mix, 6 to 12 in depth) (Utah State University Extension)
Mel's Mix resources (1/3 compost, 1/3 peat, 1/3 coarse vermiculite by volume) (Square Foot Gardening Foundation)

Next steps for this project

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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.