Garden Bed Math

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Raised bed lumber calculator

Quick answer

A 4 by 8 ft bed built two boards high from 2x6 lumber takes 6 boards of 8 ft. A 2x6 is really 1 1/2 by 5 1/2 inches under the federal lumber standard, so the bed stands 11 inches tall. Four boards stay whole for the long sides. The other two give four short sides of 45 inches, the 48 inch width less two board thicknesses. Six posts 11 inches long all come out of one 8 ft 4x4.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

Updated October 10, 2026 Sources checked October 10, 2026 Printable raised bed cut list

An unfinished two-board raised bed frame on a lawn with a tape measure along the long side

Raised bed lumber calculator

Change any number and the answer updates as you type.

Bed size
Boards

The kerf, or saw cut width, is printed on the blade's package. Leave it blank to plan exact cuts.

Posts (optional)

Side boards to buy 6 boards of 2x6, 8 ft long

Boards needed by board length
BuyingHow many
8 ft boards6 boards12 in left over
10 ft boards6 boards156 in left over
12 ft boards4 boards12 in left over
14 ft boards4 boards108 in left over
16 ft boards3 boards12 in left over
Long sides
4 at 96 in (243.8 cm)
Short sides
4 at 45 in (114.3 cm)
Bed height
11 in (27.9 cm), 2 boards of 5 1/2 in
Posts (4x4)
6 at 11 in (27.9 cm), cut from one 8 ft post
Inside the frame
93 in × 45 in
Soil to fill it
26.64 cu ft

Cut plan, board by board (8 ft boards, no saw cut allowance):

  1. 96 in
  2. 96 in
  3. 96 in
  4. 96 in
  5. 45 in + 45 in (6 in left)
  6. 45 in + 45 in (6 in left)

Oregon State Extension says beds longer than 6 ft or taller than about 18 in should be reinforced with cross cable, anchored stakes or something similar, so the soil does not push the boards out. The extra posts along the long sides are one way to do it.

No garden math needed

How to use this, in plain words

  1. Decide the bed size and whether you mean the outside of the frame or the soil inside it. Mark the corners on the ground with stakes or a garden hose if it helps.

  2. Pick the board size and how many boards high. A 2x6 is really 5 1/2 inches wide, so two of them stack to 11 inches, not 12.

  3. Type the board length you plan to buy, and the saw cut width if you know it. The table shows the count for every common length, so you can pick the one that fits your car and wastes least.

  4. Cut the short sides first, using the board-by-board plan. Measure each cut from a square end and cut on the waste side of the pencil line.

  5. Print the cut list sheet and tick off each piece as it is cut. Take the inside size and soil figure to the raised bed soil calculator next.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

What the store won't tell you

Before you start

  • Board names are nominal sizes. A 2x6 measures 1 1/2 by 5 1/2 inches, and the tool works with those real sizes.
  • The standard trims a 2x board to at least its stated length and up to 3 inches over. Plan on the stated length, as the tool does, and treat any extra as a bonus.
  • Measure the cargo space before the lumber run. Longer boards can mean fewer boards and fewer cuts, but only if you can get them home. If they won't fit, ask whether the yard cuts or delivers.
  • Oregon State Extension calls 4 ft a good maximum width, so you can reach the middle from either side. Wider beds mean stepping on the soil.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026; OSU Extension FS 270, raised bed gardening, checked October 10, 2026.

Go deeper: Inside vs outside: why a 4 x 8 raised bed holds less soil than you think · How tall to build a raised bed: real board heights and the depths extension pages give · Bags or bulk: when a cubic yard delivery is cheaper · How many tomato plants fit in a 4 x 8 raised bed · How to fill a tall raised bed without buying 2 yards of soil

The formula, in words

How it works

  1. Real board sizes from the federal lumber standard, PS 20: every 2x board is 1 1/2 inches thick, and a 2x4 is 3 1/2 inches wide, a 2x6 5 1/2, a 2x8 7 1/4, a 2x10 9 1/4 and a 2x12 11 1/4. A 4x4 post is 3 1/2 inches square.
  2. Long sides run the full outside length. Short sides fit between them: outside width minus 2 board thicknesses. If you measured the soil inside instead, the long side is the inside length plus 2 thicknesses and the short side is the inside width.
  3. Pieces: 2 long and 2 short for every board of height, times the number of beds. Height: boards high × the real board width.
  4. Boards to buy: the pieces go onto boards of the length you buy, longest first, each onto the first board with room. Every cut takes the saw cut width you enter. A piece as long as the board needs no cut.
  5. Soil it will hold: inside length × inside width × height ÷ 1,728, in cubic feet.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

Printable sheet

What to record

Write the cut list down before the lumber run and tape it to the first board. The printable sheet has one row per piece:

  • Piece: long side, short side or post
  • How many
  • Cut length
  • Board size and length it comes from
  • Cut and checked
  • Notes: knots, splits, which side faces in

Open the printable raised bed cut list

Checked by hand

Worked example

One bed 8 ft long and 4 ft wide, measured on the outside, two 2x6 boards high, built from 8 ft boards, with a 4x4 post in each corner and one more halfway along each long side.

  1. Long sides run the full 8 ft = 96 in. Short sides fit between them: 48 in − 2 × 1.5 in = 45 in.
  2. 2 boards high: 4 long pieces and 4 short pieces. Height: 2 × 5.5 in = 11 in.
  3. On 8 ft (96 in) boards: 96; 96; 96; 96; 45 + 45; 45 + 45. That's 6 boards, 12 in left over.
  4. Posts: 6 × 11 in = 66 in, cut from one 8 ft (96 in) 4x4.
  5. Soil inside: 93 × 45 × 11 = 46,035 cu in ÷ 1,728 = 26.64 cu ft.
The example bed from above, 4 x 8 ft outside, and the boards it is cut from Long side 96 in (×4)Short side45 in (×4)Inside 93 × 45 in, 11 in tall From 6 boards of 2x6, 8 ft (96 in) each:96 in96 in96 in96 in45 in45 in6 in left45 in45 in6 in left Posts: 6 × 11 in from one 8 ft 4x4
The example bed from above: four whole 8 ft boards for the long sides, two boards cut into four 45 inch short sides, and six 11 inch posts from one 4x4.

Why it may not match the bag or the store

If the answer surprises you

❓

The bed came out shorter than 12 inches

Two 2x6 boards stack to 11 inches, because each is 5 1/2 inches wide. For a full foot of height, use a 2x6 on top of a 2x8 or go to three boards.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

❓

A 16 ft board didn't make two 8 ft sides

With no saw cut it does: 96 + 96 = 192 inches. Add a 1/8 inch saw cut and the second side is 1/8 inch short. The tool shows this as soon as you enter your blade's cut width.

❓

An inside size of 4 by 8 ft won't fit 8 ft boards

The long sides cover the ends of the short ones, so they are 3 inches longer than the inside: 99 inches. Buy 10 ft boards or plan the bed 3 inches smaller.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

Other cases

Variants

🟫

Taller beds

Three 2x6 boards make a bed 16 1/2 inches tall. The same 4 by 8 ft bed then takes 9 boards of 8 ft, or 6 of 12 ft. Oregon State Extension says beds taller than about 18 inches should be reinforced.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026; OSU Extension FS 270, raised bed gardening, checked October 10, 2026.

⭕

One wide board instead of two narrow ones

A single 2x12 gives 11 1/4 inches of height with half the joints. A 4 by 8 ft frame in 2x12 takes 3 boards of 8 ft: two whole long sides and one board cut into two 45 inch ends.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

🔁

Several beds the same size

Enter how many beds you are building. The tool packs every piece across all the boards at once, so offcuts from one bed can become short sides on the next.

📏

Beds sold by inside size

Some plans and kits give the soil area, such as 4 by 8 ft inside. Pick the inside option: the frame comes out 3 inches bigger each way, and the long sides grow to 99 inches, longer than an 8 ft board.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

Where each figure comes from

Numbers this tool uses

Board ends at scale: the name (dashed) and the real dry size (filled), from PS 20 2x41 1/2 × 3 1/22 high: 7 in2x61 1/2 × 5 1/22 high: 11 in2x81 1/2 × 7 1/42 high: 14 1/2 in2x101 1/2 × 9 1/42 high: 18 1/2 in2x121 1/2 × 11 1/42 high: 22 1/2 in Each 2x board is 1 1/2 in thick. A 2x4 or 2x6 is 1/2 in narrower than its name; a 2x8, 2x10 or 2x12, 3/4 in.
Board ends at scale: the size in the name, dashed, and the real dry size from the federal lumber standard. Two boards of each stack to the height underneath.

Limitations

  • Planning estimate, not a guarantee; check each board's length and straightness at the store before you load it.
  • The board plan is a quick first-fit packing, longest pieces first. A plan worked out by hand can sometimes save a board.
  • This page covers lengths and counts only. It doesn't cover which wood to use near food crops; your county extension office can answer that.
  • Posts sit inside the corners and take up a little soil space. The soil figure ignores them.

What people learn the second year

Tips and tricks

  • Buy one spare board. A board with a big knot or a split end at the cut line is easier to swap than to work around. Return the spare if you don't use it.
  • Sight down every board. Hold each board up and look along its edge before it goes on the cart. A bowed board makes a bed that rocks and leaves gaps.
  • Cut the short sides first. If a cut goes wrong, a ruined short side can still come out of a long board. A ruined long side can't.
  • Screw into the posts. Penn State Extension's build video screws the boards into corner posts rather than into the end grain, so the wood doesn't split. (Penn State Extension, how to build a raised bed)
  • Label the pieces. Pencil L or S and the course number on each piece as you cut it. Assembly goes faster when nothing gets mixed up.

Read before the store run

Guides that go deeper

Common questions

Questions

How many 2x6 boards do I need for a 4x8 raised bed?

Six boards of 8 ft for a bed two boards (11 inches) high, measured on the outside: four whole boards for the long sides and two boards cut into four 45 inch short sides. Three boards high takes nine.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

How tall is a raised bed made from two 2x6 boards?

11 inches. A 2x6 is 5 1/2 inches wide under the federal lumber standard, so two stacked boards are 11 inches and three are 16 1/2.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

How long should the short sides of a raised bed be?

With the long sides running the full length, each short side is the outside width minus two board thicknesses. For a 4 ft wide bed in 2x lumber that is 48 minus 3, or 45 inches.

Source: NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

Does an 8 foot raised bed need extra support?

Oregon State Extension says beds longer than 6 feet or taller than about 18 inches should be reinforced, for example with cross cable or anchored stakes, so the soil doesn't push the boards out. A post halfway along each long side is one common way.

Source: OSU Extension FS 270, raised bed gardening, checked October 10, 2026.

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Sources

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