Estimate raised-bed soil mix volume, bag count, and topsoil-compost-aeration breakdown from bed size, fill depth, settling allowance, and mix profile. Use it to test different inputs quickly, compare outcomes, and understand the main factors behind the result before moving on to related tools or deeper guidance.
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Raised-bed fill planner Estimate total raised-bed mix volume, bag count, and a practical topsoil-compost-aeration split from bed size, fill depth, and settling allowance.
Bed shape
Mix profile
General raised-bed planning blend with mineral soil, compost, and a small drainage amendment.
Enter bed dimensions Add the raised-bed size, fill depth, and mix profile to estimate total fill volume, bag count, and a practical component split.
Raised-bed soil mix volume, bag count, and component planning
A raised-bed soil calculator estimates how much total fill mix a new or refreshed raised bed needs, then breaks that total into practical topsoil, compost, and aeration-amendment planning volumes. This version supports rectangular and circular beds, includes a default settling allowance, and converts the final volume into bulk and bagged buying numbers so you can plan the fill before delivery day.
What this raised-bed planner is estimating
Raised beds are not just a simple topsoil order. Most builds use some combination of screened garden soil, compost, and a lighter aeration amendment such as bark fines, coir, perlite, pumice, or another locally available material to keep the bed workable over time.
This calculator starts with the bed footprint and fill depth, adds a default 10 percent settling allowance, and then applies the selected planning blend so you can see the total quantity and the rough share of each component.
Core volume formula
The base fill volume is still area multiplied by depth. Rectangular beds use length times width, while circular beds use the area of a circle. That raw volume is then increased by the settling and trimming allowance before the mix is split into components.
For example, a 4 ft by 8 ft bed filled 12 inches deep holds 32 cubic feet before allowance, or about 1.19 cubic yards. With the default 10 percent allowance, the planned order rises to about 35.2 cubic feet or 1.30 cubic yards.
How to use the mix profiles
The blend buttons are planning profiles, not agronomy prescriptions. They help you convert one total fill number into a practical shopping list for mineral soil, compost, and a lighter amendment. The correct blend still depends on what you are growing, the drainage you need, and what the existing bed already contains.
Use the balanced profile as a general starting point for new beds, move toward the compost-rich profile if you are refreshing a hungry bed with more organic matter, and use the drainage-focused profile when you want a lighter, looser fill that drains faster.
Worked example
A 4 ft by 8 ft bed filled 12 inches deep needs about 1.30 cubic yards of finished mix once the default allowance is included. On the balanced profile, that works out to roughly 0.78 cubic yards of topsoil, 0.39 cubic yards of compost, and 0.13 cubic yards of aeration amendment.
If you compare the same total against 2 cubic foot bags, the order is about 18 bags of finished mix. That does not mean every supplier sells a complete premixed raised-bed blend in that format, but it gives you a workable retail comparison when you are buying components individually.
Frequently asked questions
How much soil do I need for a 4 x 8 raised bed?
A 4 ft by 8 ft bed filled 12 inches deep needs about 32 cubic feet of base fill, which is about 1.19 cubic yards. Adding a 10 percent settling allowance brings the planning total to about 35.2 cubic feet or 1.30 cubic yards.
Should I fill a raised bed with pure topsoil?
Usually no. Many raised beds perform better with a blend that includes mineral soil, compost, and some lighter amendment for structure and drainage. The exact mix depends on crops, drainage, and the existing bed condition.
Why does this calculator add a settling allowance?
Fresh raised-bed fills settle after watering, raking, and planting. A built-in allowance helps reduce the chance of coming up short on delivery day and gives you a more practical ordering number than the raw geometry alone.
How many bags of soil are needed for a raised bed?
That depends on the bag size you are comparing with. This calculator lets you switch between common bag sizes and shows the equivalent number of bags for the finished mix and for each component share.
