Raised Bed Soil Calculator
Filling a raised bed is one of the easiest places to overspend on soil. Too little leaves the bed underfilled and roots exposed, and too much leaves you with extra bags or a pile you did not plan for.
This raised bed soil calculator works out the volume of soil your bed holds in cubic feet, cubic yards, and cubic meters. It also shows how many bags that is for the bag size you enter, and gives an optional cost estimate from a price per bag or per cubic yard.
Below you will find how to measure a bed, how deep to fill it for different crops, ready-made volumes for common bed sizes, what to fill it with, and when bags or bulk soil make more sense.
How the Raised Bed Soil Calculator Works
The calculator multiplies the inside length, width, and depth of your bed. You can enter each measurement in feet, inches, meters, centimeters, or millimeters, and pick a preset depth of 8, 12, or 18 inches.
Volume = Length × Width × Depth
Bags = Volume in cubic feet ÷ Bag size in cubic feet
The result shows the soil volume, the number of bags to the nearest whole bag, and, if you tick the cost option, an estimated cost from your price per bag or per cubic yard. Round the bag count up when you buy, since a part bag is not sold.
Measuring Your Raised Bed Correctly
Accurate measurements are the foundation of an accurate soil estimate. A small measuring error on a deep bed can add up to several extra bags.
Measuring Length and Width
Always measure the inside dimensions of the bed, not the outer frame. Wood, metal, or stone sides take up space, so measuring the outside overstates the volume.
For a rectangular bed, measure from one inside edge to the other in both directions. For a round bed or several separate beds, use the Circular Area Topsoil Calculator or the Multi-Area Topsoil Calculator instead.
Choosing the Right Soil Depth
Depth changes the total more than any other measurement, and crops differ in how much they need. The University of Maryland Extension recommends at least 8 inches of soil for leafy greens, beans, and cucumbers, and 12 to 24 inches for peppers, tomatoes, and squash.
The Royal Horticultural Society suggests about 30 cm (12 inches) for salad crops and strawberries, and 45 cm (18 inches) or more for fruit bushes. The calculator’s 12-inch preset suits most mixed vegetable beds.
Example Raised Bed Soil Calculations
A 4 ft by 8 ft bed filled 12 inches deep holds 4 × 8 × 1 = 32 cubic feet of soil. That is 32 ÷ 27 = 1.19 cubic yards, or 16 bags of 2 cubic feet.
Fill the same bed 8 inches deep and it needs 4 × 8 × (8 ÷ 12) = 21.33 cubic feet. A 4 ft by 4 ft bed filled 10 inches deep needs about 13.33 cubic feet.
Common Raised Bed Sizes: Soil Volume and Bags
The table assumes a 12-inch fill and 2 cubic foot bags. For other depths or bag sizes, use the calculator above.
| Bed size (ft) | Depth | Soil volume | Cubic yards | Bags (2 cu ft) |
|---|---|---|---|---|
| 2 × 2 | 12 in | 4 cu ft | 0.15 | 2 |
| 3 × 6 | 12 in | 18 cu ft | 0.67 | 9 |
| 4 × 4 | 12 in | 16 cu ft | 0.59 | 8 |
| 4 × 8 | 12 in | 32 cu ft | 1.19 | 16 |
| 4 × 10 | 12 in | 40 cu ft | 1.48 | 20 |
| 4 × 12 | 12 in | 48 cu ft | 1.78 | 24 |
| 6 × 8 | 12 in | 48 cu ft | 1.78 | 24 |
| 8 × 8 | 12 in | 64 cu ft | 2.37 | 32 |
| 10 × 10 | 12 in | 100 cu ft | 3.70 | 50 |
What to Fill a Raised Bed With
There is no single correct raised bed recipe, and expert sources disagree. For deep beds built on soil, university extension and RHS recipes cluster around half to two thirds topsoil, with compost making up the rest and sometimes some sand.
The right split depends on your topsoil’s quality, your compost’s maturity, and your climate. Treat 2 parts topsoil to 1 part compost, and 1 to 1, as two reasonable starting points.
Example Splits for a 4 × 8 Bed
Here is how the 32 cubic feet of a 4 × 8 bed filled 12 inches deep divides under three common recipes.
| Recipe | Topsoil | Compost or organic matter | Sand |
|---|---|---|---|
| 2 : 1 topsoil to compost | 21.33 cu ft | 10.67 cu ft | None |
| 1 : 1 topsoil to compost | 16 cu ft | 16 cu ft | None |
| RHS 7 : 3 : 2 | 18.67 cu ft | 8 cu ft | 5.33 cu ft |
The Soil Mix Ratio Calculator splits any volume into the parts you choose. Our guide to topsoil vs garden soil vs potting soil compares the materials and shows how raised bed recipes differ by source.
Bulk Topsoil vs Bagged Soil for Raised Beds
Bags are convenient for one small bed or a site a truck cannot reach, but they cost far more per cubic yard. Bulk soil is usually cheaper for larger or several beds, as long as you have delivery access and room to unload.
Delivery fees and minimum orders change the answer for small jobs. Our guide to how much topsoil costs works out where a delivered bulk order starts to beat bags.
Should You Add Extra Soil for Settling?
Soil settles after watering, and beds rich in compost sink further as the organic matter breaks down. Oregon State Extension advises expecting settling as compost decomposes.
We could not find a reliable settling percentage to quote, so choose a margin that suits your mix. The RHS also suggests stopping about 5 cm (2 inches) below the rim, which leaves room for watering and mulch.
Common Raised Bed Soil Mistakes to Avoid
One common mistake is filling too shallow for the crops you plan to grow. Another is measuring the outside of the frame, which overstates the volume.
Mixing up cubic feet and cubic yards is a frequent ordering error, since one cubic yard is 27 cubic feet. Filling with compost alone is another, because it settles heavily and Oregon State advises against it.
When to Use a Different Calculator
This calculator is built for rectangular and square raised beds. For lawns and flat areas, use the main Topsoil Calculator, and for pots and grow bags, use the Potting Soil Calculator.
To compare delivery quotes, the Topsoil Cost Calculator adds material, delivery, and a waste allowance. To blend your own mix, use the Soil Mix Ratio Calculator.
Frequently Asked Questions
How much soil do I need for a 4 × 8 raised bed?
At 12 inches deep, a 4 × 8 ft bed holds 4 × 8 × 1 = 32 cubic feet of soil, which is about 1.19 cubic yards. That is 16 bags of 2 cubic feet, or 22 bags of 1.5 cubic feet.
How many bags of soil do I need for a raised bed?
Divide the bed’s volume in cubic feet by the bag size and round up. A 4 × 8 bed filled 12 inches deep needs 32 ÷ 2 = 16 bags of 2 cubic feet, and the calculator above does this for any size.
How deep should soil be in a raised bed?
The University of Maryland Extension recommends at least 8 inches for leafy greens, beans, and cucumbers, and 12 to 24 inches for peppers, tomatoes, and squash. The RHS suggests about 30 cm for salads and strawberries and 45 cm or more for fruit bushes.
Is topsoil good for raised beds?
Topsoil works best blended with compost rather than used alone. Extension and RHS recipes for deep beds on soil mostly use about half to two thirds topsoil, with compost and sometimes sand for the rest.
What is the best soil mix for a raised bed?
There is no single best mix, because sources disagree and climates differ. Common starting points are 2 parts topsoil to 1 part compost, 1 to 1, or the RHS recipe of 7 parts topsoil, 3 parts organic matter, and 2 parts sharp sand.
Can I fill a raised bed with potting mix or garden soil?
Potting mix is contested for raised beds: the University of Minnesota says it dries out too fast, while the University of Maryland allows soilless mix plus compost for beds on pavement. Bagged garden soil recipes vary by brand, so read the label before using it as a fill.
How much extra soil should I buy for settling?
We could not find a reliable percentage to quote, so choose a margin that suits your mix. Compost-rich mixes settle more, and the RHS suggests stopping about 5 cm below the rim.
Should I buy bags or bulk soil for a raised bed?
Bags suit one small bed or a site a truck cannot reach, while bulk is usually cheaper for larger jobs. Delivery fees and minimum orders decide the break-even point, which our topsoil cost guide works through.
Final Thoughts
Measure the inside of the bed, pick a depth that suits your crops, and let the calculator turn that into cubic feet, cubic yards, and bags. Then decide on your mix and whether bags or bulk soil suit the size of the job.
Daniel
Founder & Editor – TopSoilCalcOnline.com
Daniel is the founder and primary editor of TopSoilCalcOnline.com, a practical resource built to help homeowners, landscapers, and contractors accurately calculate topsoil, compost, and soil mix requirements. With hands-on experience in lawn preparation, raised beds, topdressing, and bulk soil planning, Daniel focuses on turning complex volume calculations into simple, reliable tools. Every calculator and guide on this site is designed to reduce material waste, prevent over-ordering, and help users plan landscaping projects with confidence and precision.