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

Multiply the inside length, width and height in feet to get cubic feet, then divide by 27 for cubic yards. A 4 × 8 ft bed 11 in deep is 4 × 8 × 11/12 = 29.3 cu ft, 1.09 cu yd, or 15 bags of 2 cu ft. Measure inside the boards, not outside, and fill to the soil height you want.

Should I add extra for settling?

That is up to you. Soil in a new bed does settle, but how much depends on the soil, the compost and how firmly it was filled, and no single figure is reliable, so this calculator builds none in. The "extra for settling" choice offers 0, 10 or 20% as your own allowance: a 4 × 4 ft bed 12 in deep is 16 cu ft and 17.6 cu ft with 10% extra, 9 bags of 2 cu ft. Many people fill, water and top up instead.

What soil mix should I put in a raised bed?

It depends on your soil, your plants and what you can buy, and sources differ. Ask Extension (the Cooperative Extension question service) suggests about 2/3 to 1/2 topsoil and 1/2 to 1/3 plant-based compost. The calculator starts at 60% topsoil, 30% compost and 10% other (sand, perlite or similar) only as an editable example; it is not a recommendation. Change the three shares to your own mix, and check with your local extension office, which knows your soils. Shares that do not add to 100% are scaled, and the page says so.

How many boards do I need for a raised bed?

Count the courses (the height ÷ the board width, rounded up), then cut 2 long sides and 2 ends for each. An 8 × 4 ft bed 11 in tall of 2 × 6 boards (5.5 in wide) has 2 courses, so 8 pieces: 4 of 96 in and 4 of 51 in. On 8 ft boards that is 8 boards, because two 51 in ends do not fit on one 8 ft board. On 10 ft boards it is 6.

Why is the end board longer than the inside width?

In this layout the end boards close the ends of the long sides, so each end board is the inside width plus the thickness of the two long sides, 2 × 1.5 in = 3 in. A 4 ft (48 in) inside width needs 51 in end boards. If you build it the other way, with the ends between the long sides, the long sides are 3 in longer and the ends are the inside width; the totals barely change.

Are 2 × 6, 2 × 8, 2 × 10 and 2 × 12 really 5.5, 7.25, 9.25 and 11.25 in wide?

Yes, for dressed, dry softwood lumber: 2-by boards are 1.5 in thick, and a 2 × 6 is 5.5 in wide, a 2 × 8 is 7.25, a 2 × 10 is 9.25 and a 2 × 12 is 11.25 in. A 4 × 4 post is 3.5 × 3.5 in and a 2 × 4 is 1.5 × 3.5 in. The sources list the references. Rough-sawn or reclaimed boards can differ, so measure what you buy.

Why is my bed taller than the height I entered?

Boards stack in whole courses. A bed 12 in tall of 2 × 6 boards takes 3 courses, which build to 16.5 in; the soil figure is for the 12 in you entered. Pick a height that is a multiple of the board width (11 in for 2 × 6, 14.5 in for 2 × 8) to build exactly that tall, or rip the top board. A taller wall needs more posts or bracing than this calculator counts; follow your plan.

What do the corner posts do, and how many are counted?

They hold the boards together at each corner. The calculator counts 4 per bed, each as long as the built height of the bed, cut from a 4 × 4 or a 2 × 4 of the stock length you picked, and packs several short posts onto one stock board: 4 posts of 11 in fit on 1 stock board (one 8 ft piece of 4 × 4 or 2 × 4 when they are 11 in each). Long beds, tall beds and wide beds may need extra posts or ties in the middle; this is a counting tool, not a structural design.

How do I work out soil for several beds?

Enter the size of one bed and the number of beds; soil and lumber are totals. Three 4 × 8 ft beds 11 in tall on 10 ft boards, with 10% extra for settling, need 96.8 cu ft (3.59 cu yd), 49 bags of 2 cu ft, 18 boards and 12 posts. At that size ordering by the cubic yard is usually cheaper than bags.

Raised Garden Bed Calculator: Soil and Lumber

A raised bed 8 ft long and 4 ft wide inside and 11 in tall holds 29.3 cu ft of soil (1.09 cu yd, about 831 litres), which is 15 bags of 2 cu ft. At 60% topsoil, 30% compost and 10% other that is 17.6, 8.8 and 2.9 cu ft. To build it from 2 × 6 boards: 2 courses, 8 boards of 8 ft (4 × 96 in; 4 × 51 in) and 4 corner posts. Soil = inside length × width × height. You can add 10 or 20% for settling if you want to; that is your choice, not a built-in figure.

Figures based on the sources listed belowUpdated 2026-10-05How we calculate

Inside length (one bed)

Inside width (one bed)

Extra for settling (your choice)

None (0%)Extra 10%Extra 20%Custom

Bed height (in)

Soil depth, 6 to 24 in. The boards stack to a whole number of courses, so the built height can be a little over this.

Number of beds

Identical beds. Soil and lumber are totals for all of them.

Board sizeNominal 2-by boards are 1.5 in thick; the width shown is the actual width.

Board stock lengthThe length you will buy. Pieces are packed onto boards of this length; see the cut list.

Corner post lumberFour posts per bed, each as tall as the built bed, cut from the same stock length.

Bag sizeUse the cu ft printed on the bag. The bag count follows the size you pick.

Topsoil share (%)

Your mix, not a recommendation: edit the three shares. Extension services suggest ranges; see the sources on this page.

Compost share (%)

Other share (sand, perlite, etc.) (%)

Price per bag (optional)

Buy 15 bags

1.09 cu yd + 0% waste = 1.09 cu yd

Or 1.09 cu yd bulk

Soil to fill the beds: 1.09 cu yd (≈ 29.3 cu ft)
Soil in litres: 831 L
Topsoil (60%): 0.65 cu yd (≈ 17.6 cu ft)
Compost (30%): 0.33 cu yd (≈ 8.8 cu ft)
Other (sand, perlite, etc.) (10%): 0.11 cu yd (≈ 2.9 cu ft)
Courses of boards: 2 courses (built height 11 in)
Boards (2 × 6 × 8 ft): 8 boards
Cut list (first-fit, inches): 4 × 96 in; 4 × 51 in
Corner posts (4 × 4, 4 per bed): 4 posts (each 11 in), 1 × 8 ft 4 × 4 to buy

How this number is calculated

1.09 cu yd (no waste added) ÷ 0.0741 cu yd per bag = 15 bags

1.1 cu yd — ~11% of a standard truck load

Shopping list

Raised garden bed soil (bagged)
Compost (bagged)
Exterior deck screws
Hardware cloth (for gophers)
Contractor wheelbarrow
Garden spade shovel

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Soil for common raised bed sizes

Inside size, soil to the stated height and no settling extra: length × width × height, in cu ft, cu yd and litres, and the bags of 2 cu ft that makes. Worked by this calculator.
Bed (inside)	Height	Soil (cu ft)	Soil (cu yd)	Litres	Bags of 2 cu ft
4 × 4 ft	6 in	8	0.3	227	4
4 × 4 ft	12 in	16	0.59	453	8
4 × 4 ft	18 in	24	0.89	680	12
4 × 8 ft	6 in	16	0.59	453	8
4 × 8 ft	12 in	32	1.19	906	16
4 × 8 ft	18 in	48	1.78	1,359	24
3 × 6 ft	6 in	9	0.33	255	5
3 × 6 ft	12 in	18	0.67	510	9
3 × 6 ft	18 in	27	1	765	14

Courses of boards by bed height and board width

Courses = height ÷ actual board width, rounded up. The boards build to courses × width, which can be taller than the soil height. Worked by this calculator.
Bed height	2 × 6	2 × 8	2 × 10	2 × 12
6 in	2	1	1	1
8 in	2	2	1	1
11 in	2	2	2	1
12 in	3	2	2	2
16 in	3	3	2	2
18 in	4	3	2	2
22 in	4	4	3	2
24 in	5	4	3	3

Boards for a 4 × 8 ft bed, 11 in tall, by stock length

2 × 6 boards, 2 courses of 2 long sides (96 in) and 2 ends (51 in), packed first-fit decreasing. Worked by this calculator; saw kerf not modeled.
Stock length	Boards to buy	Cuts per board
8 ft	8	4 × 96 in; 4 × 51 in
10 ft	6	4 × 96 in; 2 × 51 in + 51 in
12 ft	6	4 × 96 in; 2 × 51 in + 51 in
16 ft	4	2 × 96 in + 96 in; 1 × 51 in + 51 in + 51 in; 1 × 51 in

Methodology & assumptions

Soil volume is the inside length × width × height, in cubic feet, times the number of beds; ÷ 27 gives cubic yards and × 28.317 gives litres (1 cu ft = 28.316846592 L). The optional "extra for settling" is 0, 10 or 20%, picked by you: no settling figure is built in, and how much a bed settles depends on the soil, the compost and how it was filled. Bags are the soil with the extra ÷ the bag size, rounded up once for the whole job. The mix split multiplies that total by each share; if the three shares do not add to 100% the split is scaled to the total and the page says so. The posts at the corners take up about 1 to 2% of the soil space of the beds in the table and are not subtracted, so the soil figure is a little generous. Lumber: the boards stack to ceil(height ÷ board width) courses, so the built height can be up to nearly one board taller than the soil height; the soil quantity is for the height you enter, not the built height. Each course has 2 long sides, as long as the longer inside dimension, and 2 end boards, as long as the shorter inside dimension plus 2 × 1.5 in. The end boards close the ends of the long sides, butting against their end grain, so the inside dimensions come out as entered; if you build with the long sides between the ends, swap the lengths. Nominal 2-by lumber is 1.5 in thick, and the actual widths are 5.5, 7.25, 9.25 and 11.25 in for 2 × 6, 2 × 8, 2 × 10 and 2 × 12. The cut list is a first-fit decreasing packing: pieces sorted longest first, each put on the first board that still has room, otherwise a new board. A side longer than the stock length is made from a full board plus the rest, to be joined over a post. Saw kerf is not modeled, so buy a spare board or two. Corner posts: 4 per bed, each as long as the built height, packed onto the same stock length (4 × 4 or 2 × 4). Soil and lumber are estimates for planning, not a drawing: check your boards and fasteners before you cut.

Nominal Vs Actual Lumber Sizes, Southern Pine Inspection Bureau (SPIB) blog (dressed, dry sizes under the American Softwood Lumber Standard)
Lumber Dimensions: Nominal vs Actual, Archtoolbox: 2 × 6 is 1.5 × 5.5 in, 2 × 8 is 1.5 × 7.25 in, 2 × 10 is 1.5 × 9.25 in, 2 × 12 is 1.5 × 11.25 in, 4 × 4 is 3.5 × 3.5 in
American Softwood Lumber Standard, Voluntary Product Standard PS 20 (NIST): the standard that fixes the actual sizes of nominal softwood lumber
Raised garden bed soil, Ask Extension (eXtension Foundation / Cooperative Extension): suggests about 2/3 to 1/2 topsoil and 1/2 to 1/3 plant-based compost for a raised bed
Conversion: 1 cubic yard = 27 cubic feet; 1 cubic foot = 28.316846592 litres (exact, from the definitions of the foot and the litre)

How to calculate soil and lumber for a raised garden bed

Measure the inside of the bed. Decide the inside length and width and the soil depth you want, 6 to 24 in.
Work out the soil. Length × width × height in feet is cubic feet; ÷ 27 is cubic yards. Add an allowance for settling only if you want one.
Split the mix. Multiply the total by your share of topsoil, compost and anything else.
Count the courses. Divide the height by the actual board width (5.5 in for a 2 × 6) and round up.
Make the cut list. Each course takes 2 long sides and 2 ends; pack the pieces onto stock lengths, longest first.
Count the corner posts. Four per bed, each as long as the built height.

Worked examples

Project	Result
One 8 × 4 ft bed inside, 11 in tall, 2 × 6 boards on 8 ft stock, 2 cu ft bags, no settling extra	15 bags of 2 cu ft (29.3 cu ft), 2 courses, 8 boards, 4 posts
One 4 × 4 ft bed, 12 in tall, with 10% extra for settling	9 bags of 2 cu ft (17.6 cu ft), 3 courses, 9 boards, 4 posts
One 6 × 3 ft bed, 18 in tall, 2 × 8 boards	14 bags of 2 cu ft (27 cu ft), 3 courses, 9 boards, 4 posts
Three 8 × 4 ft beds, 11 in tall, 10 ft boards, 10% extra for settling	49 bags of 2 cu ft (96.8 cu ft, 3.59 cu yd), 18 boards, 12 posts
One 8 × 4 ft bed, 22 in tall, 2 × 12 boards on 12 ft stock	30 bags of 2 cu ft (58.7 cu ft), 2 courses, 6 boards, 4 posts

Frequently asked questions

How much soil do I need for a raised garden bed?: Multiply the inside length, width and height in feet to get cubic feet, then divide by 27 for cubic yards. A 4 × 8 ft bed 11 in deep is 4 × 8 × 11/12 = 29.3 cu ft, 1.09 cu yd, or 15 bags of 2 cu ft. Measure inside the boards, not outside, and fill to the soil height you want.
Should I add extra for settling?: That is up to you. Soil in a new bed does settle, but how much depends on the soil, the compost and how firmly it was filled, and no single figure is reliable, so this calculator builds none in. The "extra for settling" choice offers 0, 10 or 20% as your own allowance: a 4 × 4 ft bed 12 in deep is 16 cu ft and 17.6 cu ft with 10% extra, 9 bags of 2 cu ft. Many people fill, water and top up instead.
What soil mix should I put in a raised bed?: It depends on your soil, your plants and what you can buy, and sources differ. Ask Extension (the Cooperative Extension question service) suggests about 2/3 to 1/2 topsoil and 1/2 to 1/3 plant-based compost. The calculator starts at 60% topsoil, 30% compost and 10% other (sand, perlite or similar) only as an editable example; it is not a recommendation. Change the three shares to your own mix, and check with your local extension office, which knows your soils. Shares that do not add to 100% are scaled, and the page says so.
How many boards do I need for a raised bed?: Count the courses (the height ÷ the board width, rounded up), then cut 2 long sides and 2 ends for each. An 8 × 4 ft bed 11 in tall of 2 × 6 boards (5.5 in wide) has 2 courses, so 8 pieces: 4 of 96 in and 4 of 51 in. On 8 ft boards that is 8 boards, because two 51 in ends do not fit on one 8 ft board. On 10 ft boards it is 6.
Why is the end board longer than the inside width?: In this layout the end boards close the ends of the long sides, so each end board is the inside width plus the thickness of the two long sides, 2 × 1.5 in = 3 in. A 4 ft (48 in) inside width needs 51 in end boards. If you build it the other way, with the ends between the long sides, the long sides are 3 in longer and the ends are the inside width; the totals barely change.
Are 2 × 6, 2 × 8, 2 × 10 and 2 × 12 really 5.5, 7.25, 9.25 and 11.25 in wide?: Yes, for dressed, dry softwood lumber: 2-by boards are 1.5 in thick, and a 2 × 6 is 5.5 in wide, a 2 × 8 is 7.25, a 2 × 10 is 9.25 and a 2 × 12 is 11.25 in. A 4 × 4 post is 3.5 × 3.5 in and a 2 × 4 is 1.5 × 3.5 in. The sources list the references. Rough-sawn or reclaimed boards can differ, so measure what you buy.
Why is my bed taller than the height I entered?: Boards stack in whole courses. A bed 12 in tall of 2 × 6 boards takes 3 courses, which build to 16.5 in; the soil figure is for the 12 in you entered. Pick a height that is a multiple of the board width (11 in for 2 × 6, 14.5 in for 2 × 8) to build exactly that tall, or rip the top board. A taller wall needs more posts or bracing than this calculator counts; follow your plan.
What do the corner posts do, and how many are counted?: They hold the boards together at each corner. The calculator counts 4 per bed, each as long as the built height of the bed, cut from a 4 × 4 or a 2 × 4 of the stock length you picked, and packs several short posts onto one stock board: 4 posts of 11 in fit on 1 stock board (one 8 ft piece of 4 × 4 or 2 × 4 when they are 11 in each). Long beds, tall beds and wide beds may need extra posts or ties in the middle; this is a counting tool, not a structural design.
How do I work out soil for several beds?: Enter the size of one bed and the number of beds; soil and lumber are totals. Three 4 × 8 ft beds 11 in tall on 10 ft boards, with 10% extra for settling, need 96.8 cu ft (3.59 cu yd), 49 bags of 2 cu ft, 18 boards and 12 posts. At that size ordering by the cubic yard is usually cheaper than bags.

Handy tools

Board Foot Calculator: Price the boards by the board foot, or compare a 2 × 6 with a 2 × 8 or 2 × 10 for the same bed.