Raised Bed Soil Mix: Published Ratios
Extension services publish different raised bed soil mixes: Iowa State gives about 70%[1] topsoil and about 30%[1] compost, and the others are in the table with the cubic yards of each part for a bed.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Raised Bed Soil CalculatorEach published mix, in cubic yards of each part
Cubic yards of compost, topsoil or soil, and other parts for a four by eight foot bed at a twelve inch fill, for each published recipe
| Source and recipe | Compost | Topsoil or soil | Other parts together |
|---|---|---|---|
| Iowa State: seventy percent topsoil, thirty percent compost | 0.36 yd³ | 0.83 yd³ | 0 yd³ |
| Iowa State: equal parts topsoil, organic matter and coarse sand | 0 yd³ | 0.4 yd³ | 0.79 yd³ |
| Minnesota: two thirds topsoil, one third compost | 0.4 yd³ | 0.79 yd³ | 0 yd³ |
| Minnesota: equal parts topsoil and compost | 0.59 yd³ | 0.59 yd³ | 0 yd³ |
| Maryland: one part compost, two parts topsoil | 0.4 yd³ | 0.79 yd³ | 0 yd³ |
| Maryland: equal parts compost and topsoil | 0.59 yd³ | 0.59 yd³ | 0 yd³ |
| Maryland: equal parts compost and soilless mix | 0.59 yd³ | 0 yd³ | 0.59 yd³ |
| Utah State: equal parts compost, drainage material and soil | 0.4 yd³ | 0.4 yd³ | 0.4 yd³ |
| Clemson: compost is ten percent of the bed volume | 0.12 yd³ | 1.07 yd³ | 0 yd³ |
| Clemson: compost is twenty percent of the bed volume | 0.24 yd³ | 0.95 yd³ | 0 yd³ |
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Each recipe is the one its source prints, split exactly over the bed's volume. The sources differ, and none of them is a rule.
What each extension publishes
An excellent soil mix can be prepared by mixing equal parts topsoil, organic matter (well-rotted manure, compost, or peat), and coarse sand. Another option is ~70% topsoil and ~30% compost.
The ideal soil mixture for a raised bed is a mixture of around 2/3 to 1/2 topsoil and 1/2 to 1/3 plant-based compost. If the topsoil contains a lot of clay, you may also add some sand to create a more loamy soil texture.
Add a mixture of compost and purchased topsoil in a 1:2 or 1:1 ratio, to the top of the bed. ... Alternatively, fill the bed with compost and a soilless growing mix in a 1:1 ratio.
A garden soil blend could consists of equal parts (1:1:1 by volume), of the following ingredients: ... Native soil or topsoil
The amount of compost added should be in a range of 10-20% of the total volume (length x width x height) of medium added to the bed.
The organic matter (OM) content in a raised bed containing garden soil, should be 25%-50% by volume or 5%-15% by weight (as measured by a soil testing lab).
The compost share
Clemson gives compost as a share of the bed volume, while Iowa State, Minnesota and Maryland give it as a share of the mix with topsoil. The compost calculator turns any share into cubic yards or bags.
Topsoil in tall beds
Maryland limits topsoil by volume in beds that are deep enough, and gives a deeper bed depth for each crop; the quotation above has both figures. The raised bed soil calculator takes your own depth.
Questions
What soil mix does each extension publish for a raised bed?
The table lists every recipe with the cubic yards of each part for a four by eight foot bed, and the quotations under it print each source's own words.
How much compost goes in a raised bed?
It depends on the source: some give compost as a share of the mix with topsoil and one gives it as a share of the whole bed. The table shows the compost yards each recipe gives.
Is topsoil used in tall raised beds?
Maryland Extension gives a topsoil limit for deep beds, quoted with its figure above. The calculator splits your bed by whichever recipe you choose.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Raised Bed Soil CalculatorSources (5)
-
What would be a good soil mix for a raised bed? (Yard and Garden FAQ) (opens in new tab), Iowa State University Extension and Outreach, updated April 20, 2026.
Code or government.
“An excellent soil mix can be prepared by mixing equal parts topsoil, organic matter (well-rotted manure, compost, or peat), and coarse sand. Another option is ~70% topsoil and ~30% compost.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1) -
Raised bed gardens (opens in new tab), University of Minnesota Extension, page states "Reviewed in 2026".
Code or government.
“The ideal soil mixture for a raised bed is a mixture of around 2/3 to 1/2 topsoil and 1/2 to 1/3 plant-based compost. If the topsoil contains a lot of clay, you may also add some sand to create a more loamy soil texture.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 2) -
Soil to Fill Raised Beds (opens in new tab), University of Maryland Extension (J. Traunfeld), updated November 6, 2024.
Code or government.
“Add a mixture of compost and purchased topsoil in a 1:2 or 1:1 ratio, to the top of the bed. ... Alternatively, fill the bed with compost and a soilless growing mix in a 1:1 ratio.”
“Topsoil can be added (up to 20% by volume) for beds that are at least 16 inches deep.”
“The organic matter (OM) content in a raised bed containing garden soil, should be 25%-50% by volume or 5%-15% by weight (as measured by a soil testing lab).”
“Raised bed gardens placed on hard surfaces are fine if they are a minimum of 8 inches deep for leafy greens, beans, and cucumbers, and 12-24 inches deep for pepper, tomato, and squash.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 3) -
Raised Bed Gardening (peer-reviewed fact sheet) (opens in new tab), Utah State University Extension, Published February 2012.
Code or government.
“A garden soil blend could consists of equal parts (1:1:1 by volume), of the following ingredients: ... Native soil or topsoil”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 4) -
Raised Beds (HGIC 1257) (opens in new tab), Clemson Cooperative Extension, Home and Garden Information Center, revised Aug 1, 2017.
Code or government.
“The amount of compost added should be in a range of 10-20% of the total volume (length x width x height) of medium added to the bed.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 5)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.