A “2×6” board is really 5½ inches wide, so beds come out shorter than people expect. Enter your bed size, board size, and how many boards high you will stack, and this calculator gives the boards to buy, a cut list, the real bed height, and the soil it will hold.
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What Your Result Means: the board count is how many full-length boards to buy, with the cuts packed to limit waste. The height is the real height from actual board widths, and the soil figure is the space inside the finished frame.
How Much Lumber Do You Need for a Raised Bed?
An 8 by 4 foot bed two 2×6 boards high takes six 8-foot boards and stands 11 inches tall. Enter your own bed size, board size, and rows, and the tool works out the boards, cuts, corner posts, screws, and soil.
- Enter the Bed Size, the outside length and width in feet.
- Choose the Boards, the size and how many rows high.
- Pick the Board Length sold at your store, and read the shopping list.
What Each Result Means
| Result | What It Tells You |
|---|---|
| Boards to buy | Full-length boards needed |
| Cut list | Each piece and how many |
| Real height | Bed height from actual board widths |
| Soil to fill | Cubic feet and yards inside the frame |
Actual Board Sizes
Lumber is named by its rough size before drying and planing. The actual dry sizes are smaller.
| Board | Actual Size | Bed Height per Row |
|---|---|---|
| 2×6 | 1½ x 5½ in | 5½ in |
| 2×8 | 1½ x 7¼ in | 7¼ in |
| 2×10 | 1½ x 9¼ in | 9¼ in |
| 2×12 | 1½ x 11¼ in | 11¼ in |
How Is the Lumber Worked Out?
The long sides run the full length, and the short sides fit between them, so each short piece is the width minus two board thicknesses (3 inches). The tool lists every piece for every row, then packs them onto your board length, longest first, to use as few boards as possible.
Height = rows x actual board width
Boards = pieces packed onto your board length, longest first
Soil (cu ft) = (length – 3 in) x (width – 3 in) x height / 1728
The soil figure uses the inside of the frame, since the boards themselves take up space.
Worked Example
Say you build an 8 by 4 foot bed two 2×6 boards high, buying 8-foot boards. Each row needs two 8-foot pieces and two pieces 3 feet 9 inches long. Across both rows, that is 6 boards: four used whole, and two each cut into a pair of short pieces. The bed stands 11 inches tall and holds about 26.6 cubic feet of soil, just under a cubic yard.
Choosing Wood for a Vegetable Bed
- Cedar or redwood: naturally rot-resistant and a common choice for food beds.
- Modern treated lumber: copper-based treatments such as ACQ are considered acceptable by extension services.
- Avoid creosote and penta: railroad ties and wood treated with these are not for vegetable beds.
- Old CCA wood: arsenic-based treatment was phased out of home use at the end of 2003; line or seal old boards if you reuse them.
- Other options: recycled plastic lumber, blocks, brick, or stone last longer but cost more.
Understanding Your Outputs
| Output | Meaning | Best Used For |
|---|---|---|
| Boards to buy | Full-length boards | Your shopping list |
| Cut list | Pieces and lengths | Cutting at home or the store |
| Corner posts | Four posts cut to height | Joining the corners |
| Soil to fill | Inside volume | Ordering soil |
When to Use It
Use it before a trip to the lumber yard, to choose a board size and length that wastes the least. Pair it with the raised-bed soil volume calculator for a soil mix and the plant spacing calculator to see how many tomatoes fit.
Common Mistakes to Avoid
- Using nominal sizes: two 2×6 rows make an 11-inch bed, not 12.
- Forgetting the short-side deduction: short pieces are 3 inches shorter than the bed width.
- Building too wide: keep beds 4 feet or less so you can reach the middle without stepping in.
- Skipping mid-side bracing: soil pushes long sides outward; brace sides longer than about 8 feet.
- Too shallow for tomatoes: 10 to 12 inches is the general minimum, but tomatoes do best with 12 inches or more (18 is better).
Accuracy and Limitations
The math follows standard lumber sizes and a simple butt-joint frame.
What It Calculates: boards, cuts, height, posts, screws, and soil for a four-sided frame.
What It Does Not Include: saw kerf, damaged ends, or other joint styles. Buy one spare board for longer beds or rough lumber.
Methodology
Method: each row needs two long pieces equal to the bed length and two short pieces equal to the bed width minus 3 inches, since the short sides sit between the 1½-inch-thick long boards. All pieces are packed onto the chosen board length, longest first, and each new board is started only when no existing offcut is long enough. Board sizes: dry dressed widths from the American Softwood Lumber Standard: 2×6 = 5½ in, 2×8 = 7¼ in, 2×10 = 9¼ in, 2×12 = 11¼ in, thickness 1½ in. Height: rows times actual width. Soil: inside length times inside width times height. Screws: an estimate of 2 exterior screws per board end for 2×6 and 3 for wider boards, into four corner posts. Guidance: 10 to 12 inches of soil as a general minimum, 12 inches or more for tomatoes, and a width of 4 feet or less when reached from both sides.
Sources: NIST – American Softwood Lumber Standard PS 20, Purdue Extension – Container and Raised Bed Gardening, University of Georgia CAES – Raised Beds. Last reviewed: September 26, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
How many boards do I need for a 4×8 raised bed?
Two rows of 2×6 boards take six 8-foot boards: four used whole for the long sides and two cut into four short pieces. The bed stands 11 inches tall.
How tall is a raised bed made of two 2×6 boards?
11 inches, not 12. A 2×6 is actually 5½ inches wide, so two stacked rows make 11 inches.
How deep should a raised bed be for tomatoes?
At least 12 inches of soil for tomatoes, and 18 inches is better; 10 to 12 inches is the general minimum for vegetables. Tomato roots can reach 2 to 3 feet, so a deeper bed or loosened soil underneath helps.
Is pressure-treated wood safe for vegetable beds?
Modern copper-based treatments such as ACQ are considered acceptable by extension services. Avoid creosote, penta, and railroad ties, and consider lining old CCA-treated wood.
What is the best wood for a raised bed?
Cedar and redwood resist rot naturally and are popular for food beds. Treated lumber is cheaper and lasts well; recycled plastic lumber lasts longest.
How wide should a raised bed be?
Up to 4 feet if you can reach it from both sides, or about 2 feet against a wall or fence, so you never need to step into the bed.
Why are my short boards shorter than the bed width?
They sit between the long boards, which are each 1½ inches thick, so each short piece is 3 inches shorter than the outside width.
How much soil does a 4×8 raised bed hold?
An 11-inch-tall frame holds about 26 to 27 cubic feet inside, just under one cubic yard.
Do I need corner posts?
They make a sturdier frame and give the screws solid wood to bite into. Cut four posts to the bed height from 2×4 or 4×4 lumber.
Related Tomato Tools
Work Out Your Soil Mix with the Soil Volume Calculator
This calculator gives a lumber estimate for a simple four-sided frame using standard board sizes. It does not include saw kerf or damaged ends, so buy a spare board for larger beds. Wear eye protection when cutting and follow the tool maker’s safety instructions. Spotted an error? Tell us here.