How to use the raised bed soil calculator
Enter the inside length and width of a bed, how deep you'll fill it and how many beds of that size you have. The calculator adds a little for settling, then splits the total into your blend. Enter the percentages you want for topsoil, compost and anything else; they should add up to 100.
The formula
cubic feet = length × width × depth (ft) × beds × (1 + settling)
each ingredient = total × its percentage
bags = cubic feet ÷ bag size, rounded up
Worked example: two 8 × 4 ft beds, 12 inches deep
- One bed: 8 × 4 × 1 = 32 ft³. Two beds: 64 ft³.
- Plus 10% for settling: 70.4 ft³, or 2.61 yd³.
- At 60/40: 42.2 ft³ of topsoil and 28.2 ft³ of compost.
- In 1.5 ft³ bags: 70.4 ÷ 1.5 = 47 bags. At this size, bulk delivery is worth pricing.
Bed sizes at a glance
| Bed | Depth | Soil |
|---|---|---|
| 4 × 4 ft | 12 in | 16 ft³ (0.59 yd³) |
| 4 × 8 ft | 12 in | 32 ft³ (1.19 yd³) |
| 4 × 8 ft | 18 in | 48 ft³ (1.78 yd³) |
| 3 × 6 ft | 12 in | 18 ft³ (0.67 yd³) |
Before settling allowance. Use the inside dimensions: walls built from 2× lumber take 1½ in off each side.
Filling tips
- Tall beds (over about 18 in) don't need premium soil all the way down. Some gardeners fill the bottom with logs, branches or leaves and top with soil, which settles over time.
- Loosen the ground under the bed so roots and water can move down.
- Top up yearly with an inch or two of compost as the soil settles and breaks down.
- Check the bag: bagged "garden soil" and "raised bed mix" vary. Look for weed-free, screened products.
Questions people ask
How much soil do I need for a 4x8 raised bed?
A 4 × 8 ft bed 12 inches deep holds 32 cubic feet, which is 1.19 cubic yards: 16 bags of 2 cubic feet or 22 bags of 1.5 cubic feet. At 10 inches deep (a 2 × 10 board's height, about 9¼ in actual) it's closer to 25 cubic feet.
How many bags of soil fill a raised bed?
Divide the bed's volume in cubic feet by the bag size. Bags are labeled in cubic feet or quarts; 1 cubic foot is about 25.7 quarts. Add about 10% because fresh soil settles.
Is it cheaper to buy raised bed soil in bags or bulk?
Past about a cubic yard (27 cubic feet), bulk soil from a landscape yard is usually much cheaper per cubic foot than bags, even with delivery. For one or two small beds, bags are easier.
What soil mix should I use in a raised bed?
Most gardeners use a blend of good topsoil and compost, sometimes with an ingredient for drainage and water holding. Your local extension service can recommend a mix for your area and crops; this calculator splits the volume into whatever proportions you choose.
How deep should a raised bed be?
8 to 12 inches suits most vegetables and flowers. Deep-rooted crops like tomatoes and carrots appreciate 12 inches or more, especially if the ground underneath is poor.
Sources and assumptions
- 1 ft³ = 1,728 in³ ≈ 25.7 US dry quarts; 27 ft³ = 1 yd³ (NIST Handbook 44)
- The default 60/40 topsoil and compost split is only an example; set your own blend. The 10% settling allowance is a rule of thumb.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.