How much soil do I need for a raised bed?

The arithmetic, and why this one is bigger than it looks

Inside length times inside width times depth. Measure inside the boards, not outside, because the lumber thickness is not soil. The eight by four box this page opens with, filled twelve inches deep, is 32 cubic feet. In one and a half cubic foot bags that is 21.3, so 22 bags. In three quarter cubic foot bags it is 43. In cubic yards, at 27 cubic feet to the yard from NIST Handbook 44, it is 1.19.

That last figure is the one that surprises people. A single ordinary raised bed is more than a cubic yard of material. It is the same volume as a concrete pad, and it arrives in bags that weigh what a bag of concrete weighs. Four boards and a Saturday is the accurate description of building the box. Filling it is a different afternoon.

How much extra is technical, and how much is next year's purchase

Filling a box has no cut waste at all, so this page starts you at zero extra, and it stays there unless you put a number in yourself.

What is real is settling, and it is not a fill-day problem. University of Illinois Extension calls settling soil simply a fact of raised bed gardening, caused by poor structure and by the gardener disturbing the bed, and its remedy is annual: topdressing with a few inches of compost or good topsoil each year should be enough to keep up with the settling level. That is a purchase you make next spring, from a different aisle, in a smaller quantity. Adding fifteen percent to today's order to pre-pay for it means storing wet bags in a garage for eight months, which is not the same thing as buying compost when you need it.

The point where the number you were given stops adding up

Multiply the bags quoted by the cubic feet declared on the bag, and compare against your box volume. Twenty two bags at 1.5 is 33 cubic feet against a 32 cubic foot box, which is the rounding and nothing more. Thirty bags at the same size is 45 cubic feet against the same box, forty percent over, and that is a conversation.

Then there is the flag that is specific to soil and does not exist on the mulch page. If the bag in front of you declares only a weight, you cannot run this test at all. Forty pounds is not a volume. The same forty pounds holds noticeably less material when the pallet has been sitting in the rain, because you are paying for the water. Look for a bag that declares cubic feet, and if the shelf offers you a choice between a bag priced by weight and a bag priced by volume, the one you can do arithmetic with is the one you can compare.

The regulation covers mulch and peat, and stops short of your soil

This is worth knowing precisely, because it is the difference between the two garden pages on this site. NIST Handbook 130 requires all mulch to be sold by volume, but it defines mulch in section 2.18.1.1 as any product except peat or peat moss sold primarily as an aboveground dressing. A bagged raised bed mix or garden soil is not that. It is the thing the plants grow in, not a dressing laid on top.

Peat does have its own rule. Section 2.5.2.2 says peat and peat moss sold by cubic measure must be offered in liters or cubic feet, and that if it is labeled in compressed cubic measurement the declaration represents the quantity in the compressed state. Most bed mixes contain peat or coir, and compressed bales are common, so this matters in your favor for once: a compressed bale declares less volume than it will occupy after you open it and break it up. Nobody publishes the expansion ratio, so you cannot calculate with it, but you should not assume a compressed bale and a loose bag of the same declared volume are the same purchase.

One bed sits exactly where bulk delivery is least convenient

Bulk soil is cheaper per cubic foot than bagged soil and it comes with a delivery fee and usually a minimum load. The arithmetic that decides it is not complicated, but the shape of the answer for raised beds is unusual and worth saying plainly: a single bed is almost never the case where bulk wins, and three beds almost always is.

Look at why. One eight by four bed at twelve inches is 1.19 yards. If the supplier's smallest delivery is one yard and they sell in whole yards, you are ordering two and paying to store the leftover. Two beds is 2.37 yards, so three yards ordered. Three beds is 3.56 yards, which is four ordered and only a small fraction wasted, and by then the delivery fee has been divided across enough material to disappear.

To settle it with your own numbers rather than an average, do this at the counter. Divide 27 by the cubic feet on your bag to get bags per yard, which is 18 for a one and a half cubic foot bag and 13.5 for a two. Multiply by the bag price. That is one yard's worth of soil bought in bags. If it is smaller than the bulk price of a yard, bulk cannot win no matter how many yards you buy. If it is larger, the difference is your saving per yard, and the delivery fee divided by that saving is the number of yards at which the truck becomes the cheaper choice. The price fields above run this for you the moment you fill them in.

One thing the arithmetic will not tell you. Bulk soil arrives as one pile at the end of your driveway and every cubic foot of it is moved by you with a wheelbarrow, while a bag can be carried by one person and left sealed until you are ready. That is worth different amounts to different backs.

The box itself, which is a different piece of arithmetic entirely

Everything above this line is volume. The frame is not, and that is worth saying plainly, because cubic feet of soil tells you nothing whatsoever about how many boards to buy. The frame is decided by the distance around the box and by how wide one board actually is, and the count above works it out in four steps you can check on your fingers.

Take the eight by four bed this page opens with. Twice eight plus four is twenty four feet of perimeter, and that is true for one course of boards. Now the part that catches people. A board is never as wide as its name. NIST Voluntary Product Standard PS 20, the federal softwood lumber standard, sets the minimum dressed dry width: a nominal six inch board finishes at five and a half inches, a nominal eight at seven and a quarter, a ten at nine and a quarter, a twelve at eleven and a quarter. So a twelve inch deep bed built from two by eights is twelve divided by seven and a quarter, which is one and two thirds, which rounds up to two courses. Not one and a half. Two.

Twenty four feet of perimeter times two courses is forty eight linear feet of board. At eight foot lengths that is six boards exactly, which is the number the page prints, and it is exact because an eight foot board is precisely one long side and two eight foot boards are precisely the two short sides plus a spare foot. Buy ten foot boards for the same bed and you are paying for twenty four feet of offcut. That single choice is the whole difference between a tidy purchase and a pile of scrap, and no volume calculation anywhere will ever tell you about it.

The screws follow the courses rather than the soil. Four corners, one joint per course, three screws a joint, so a two course bed is twenty four screws and one box covers it with plenty over. Note that the field for screws per box is marked as your number, because boxes run anywhere from fifty to five hundred and nobody standardised it.

One honest limit. This counts a rectangle sitting on level ground. A bed on a slope needs the low side taller, and this page will not tell you by how much, because that depends on a fall nobody here can measure for you.

What it still does not count

• The corner posts, if you want them. The board count above assumes the ends are screwed straight into the sides. Add four posts and the cut list changes, and so does the rigidity once thirty two cubic feet of wet soil starts pushing outward.
• Hardware cloth for the bottom, if you have voles or gophers. It is cheap the day you build and impossible the day after you fill.
• The annual topdressing. A few inches of compost every spring is the Extension's answer to settling, and on an eight by four bed a two inch topdress is 5.3 cubic feet. That is a real recurring line, not a one time cost.
• Amendments and the difference between three products. Topsoil, garden soil and raised bed mix are sold side by side at three prices and they are not interchangeable. This page counts volume and does not judge which of them belongs in your bed.

Where the bag price above comes from, and what it leaves out

The conversions on this page are federal and definitional. The peat labeling rule is a published uniform regulation. The settling guidance comes from a land grant university with a named author and a date. The dollar range is none of those things, so it is read a fourth way: off product pages at Sutherlands, a home improvement and lumber chain out of Kansas City, Missouri whose pages publish a price for every one of its stores instead of one national number. Three bags were read on 2026-08-23, picked to span the shelf rather than to flatter the total:

• hapi-gro organic raised bed planting mix, 1.5 cubic feet, item 2641629: 8.49 to 9.99 dollars across the 6 stores with it in stock. Open the product page.
• Miracle-Gro raised bed soil, 1.5 cubic feet, item 312199: 11.99 to 16.99 dollars across the 7 stores with it in stock. Open the product page.
• Miracle-Gro all purpose garden soil, 1.5 cubic feet, item 4230926: 7.99 to 16.99 dollars across the 25 stores with it in stock. Open the product page.

That spread, 7.99 to 16.99 for the same cubic foot and a half, is not noise. Garden soil and a proper raised bed mix are different products at different money, and the range on this page deliberately covers both rather than quietly picking the cheap one. Filling a bed this way is expensive, and seeing the real top of the range is the point at which most people go and price a bulk load instead.

The frame is read the same way, off the same kind of page, on the same date:

• Sutherlands 2 in. by 8 in. by 8 ft. number 2 S4S treated yellow pine, item 16758: 11.19 to 13.79 dollars across the 9 stores with it in stock. Open the product page.
• Sutherlands 2 in. by 8 in. by 10 ft. number 2 S4S treated yellow pine, item 16766: 13.46 to 16.29 dollars across the 8 stores with it in stock. Open the product page.
• Hillman Deck Plus black square drive deck screw, number 10 by 2-1/2 in, 73 per box, item 913509: 11.99 dollars across the 33 stores with it in stock. Open the product page.
• Grip-Rite Prime Guard Ten exterior screws, 1-5/8 in, 1 pound, item 6622336: 9.99 to 16.99 dollars across the 14 stores with it in stock. Open the product page.

Those two are treated yellow pine, and that is the cheap end of the frame on purpose. Cedar is the board most people actually want for a bed and it costs considerably more, redwood more again, and composite more still. So read the board line as the floor of what a frame costs, not the price of the one you have in mind. The screw readings cover both the way this is usually sold, by the box of a stated count and by the pound.

One figure this page still refuses to print, and it is the one that would change the answer most: bulk soil delivered by the cubic yard. That is a quote from a yard, tied to your address and the size of the load, and nobody publishes it anywhere a person could cite. That field stays empty and yours. Type the tag in front of you into any price field on this page and everything reruns on your number.

Sources. NIST Handbook 44 (2026), Appendix C, nvlpubs.nist.gov, opened 2026-08-23, for 27 cubic feet to the cubic yard. NIST Handbook 130 (2026), sections 2.5.2.2 and 2.18.1.1, doi.org/10.6028/NIST.HB.130-2026, opened 2026-08-23, for the peat labeling rule and the definition of mulch. Chris Enroth, University of Illinois Extension, Refreshing raised bed soil generates exceptional results, published 5 April 2021, extension.illinois.edu, opened 2026-08-23, for settling and annual topdressing. Sutherlands, the seven product pages linked above, read 2026-08-23, for the soil, board and screw ranges.