How this planner works
- Raised beds. Inside length × inside width × fill depth (inside height minus 1 inch), with all dimensions converted to feet. Multiply by the bed count and add the selected allowance. For a blend, round bags up separately for each ingredient.
- Lumber. Rows of boards = bed height ÷ 5.5" (the real face of a 2×6), rounded up. Each side uses one 8 ft board per row, or more for sides longer than 8 ft. Four corner posts per bed.
- Mulch. Area × depth. Bags are 2 or 3 cu ft. Pine straw bales cover roughly 45 sq ft at about 3".
- Topsoil and fill. Area × depth plus settling (15% by default), with weight at about 1.1 tons per yard for topsoil and 1.2 for fill dirt. Real weights vary a lot with moisture.
Reference guidance:University of Minnesota Extension raised bed guidance. Confirm material coverage and specifications with your supplier.
Worked examples
Two 4 × 8 ft beds, 11" tall, 60/40 mix: 53.3 cu ft to fill, 58.7 cu ft with 10% for settling (2.17 cubic yards). That is 35.2 cu ft of topsoil and 23.5 cu ft of compost: 40 bags of 1.5 cu ft, or one bulk delivery. Lumber: 16 boards of 2×6×8 ft and 8 corner posts.
200 sq ft of beds mulched 3" deep: 50 cu ft = 1.85 cubic yards, or 25 bags of 2 cu ft.
Frequently asked questions
How much soil do I need for a 4×8 raised bed?
A 4×8 bed 11 inches tall (two 2×6 boards), filled to an inch below the top, holds about 26.7 cubic feet. With 10% extra for settling, that is roughly 29 cubic feet, or about 1.1 cubic yards. That is 20 bags of 1.5 cubic feet.
What is the best soil mix for raised beds?
A simple, widely used mix is about 60% screened topsoil and 40% compost. Some gardeners prefer equal parts topsoil, compost and an aerating material such as perlite, pumice or coarse bark. Bagged raised-bed mixes are the easiest for one or two small beds. Avoid filling beds with plain garden soil or fill dirt alone.
Is bagged or bulk soil cheaper?
For one small bed, bags are often simpler. Once you need more than about a cubic yard (27 cubic feet), bulk soil from a landscape supplier is usually much cheaper per yard, even with a delivery fee. The planner compares both with your prices.
How deep should mulch be?
Two to three inches is a common depth for garden beds: enough to hold moisture and block weeds. Deeper than about 4 inches can keep water and air from reaching roots. Keep mulch a few inches away from tree trunks and plant stems.
How much does a bag of mulch cover?
A standard 2 cubic foot bag covers about 12 square feet at 2 inches deep, or 8 square feet at 3 inches. A cubic yard covers about 162 square feet at 2 inches, or 108 square feet at 3 inches.