Peat Moss Calculator
A peat moss calculator converts bed area and depth to 6 cu ft expanded bales: a 10 × 10 ft bed amended 2 in deep takes 2.78 bales, so buy 3, about $36 at $12.
Peat moss calculator: bales from area and depth
A peat moss calculator turns the area of your bed and the depth of the layer you plan to spread into cubic feet, then divides by 6 cubic feet, the expanded volume of one bale. A 10 × 10 ft bed with a 2 inch layer needs 16.67 cubic feet, which is 2.78 bales. Since bales are sold whole, you buy 3.
The calculator rounds up to a whole bale and prices the order at the per-bale cost you enter.
The formula in plain words
Cubic feet = length × width × (depth in inches ÷ 12). Bales = cubic feet ÷ 6, rounded up. The 6 cu ft figure assumes the bale has been fluffed and dampened, so confirm the yield printed on your bag.
Worked example, a new vegetable bed
The bed measures 10 ft × 10 ft. You will spread a 2 inch layer and dig it in. A bale costs $12.
- Depth: 2 ÷ 12 = 0.1667 ft
- Volume: 10 × 10 × 0.1667 = 16.67 cubic feet
- Bales: 16.67 ÷ 6 = 2.78
- Rounded up: 3 bales
- Cost: 3 × $12 = $36
You will have about 1.3 cubic feet left over. Use it on another bed or keep it dry in the bag.
Worked example, a thicker layer
The same bed amended 3 inches deep for heavy clay.
- Volume: 10 × 10 × 0.25 = 25 cubic feet
- Bales: 25 ÷ 6 = 4.17, rounded up to 5
- Cost: 5 × $12 = $60
One extra inch adds two bales to the order. That is the effect of rounding up on a 4.17 result. If you can live with 4 bales, you will be about 1 cubic foot short.
Bales by bed size
| Bed size | Depth | Cubic feet | Bales to buy |
|---|---|---|---|
| 5 × 5 ft | 2 in | 4.17 | 1 |
| 4 × 8 ft | 2 in | 5.33 | 1 |
| 10 × 10 ft | 2 in | 16.67 | 3 |
| 20 × 10 ft | 2 in | 33.33 | 6 |
| 20 × 20 ft | 2 in | 66.67 | 12 |
How to measure
- Measure the planting area on the ground, since the amendment goes where the roots will be.
- For beds with curved edges, break them into rectangles and add the volumes.
- Decide the depth before you buy. Peat is usually spread as a layer and then dug in, so the layer thickness is what you enter.
- Loosen and dampen one bale and measure it if you want to test the stated yield.
Common mistakes
- Treating the compressed bale as the volume. A bale looks small in the store, but opens up to several times that size.
- Spreading it dry. Dry peat repels water, so wet it as you fluff it.
- Using peat on everything. It lowers pH, which suits some plants and hurts others.
- Skipping the working-in step. A layer left on top forms a crust that sheds rain.
- Buying exactly the calculated bales. Rounding the count up gives some margin for uneven digging.
Mixing it in
Open the bale in a wheelbarrow and wet it a little at a time while you break up the clumps. The goal is damp and fluffy, not soggy. Spread it over the bed in the thickness you entered, then work it into the top 6 to 8 inches with a fork or tiller.
If you are filling a container or raised bed from scratch, peat moss is usually only one part of the mix. A common recipe uses it together with compost and a coarse material such as perlite or sand, but follow the recipe for what you grow. In that case, work out the total volume of the bed first, then take only the fraction that is peat. For the 16.67 cubic foot bed, a mix with one third peat needs about 5.6 cubic feet, which is fewer than one bale.
Related pages
Compost is a common alternative or partner, and the compost calculator sizes it. For filling a whole bed with prepared soil, see the garden soil calculator. Potting blends have their own math in the potting soil calculator.
Frequently asked questions
What is peat moss?
It is partly decayed sphagnum moss harvested from bogs, dried and compressed into bales. It holds a lot of water and loosens heavy soil, so gardeners use it to amend beds and mix potting blends.
Why does one bale cover so much once it is opened?
The bale is compressed for shipping. When you fluff it and add water, it expands. This calculator uses 6 cubic feet of expanded volume per bale. Check your bale's label, since brands list different yields.
Does peat moss change soil pH?
Yes, it is acidic, so it can lower the pH of soil a little. That helps acid-loving plants like blueberries and azaleas. For plants that prefer neutral soil, check pH after you add it.
Is peat moss the same as coco coir?
No. Coir is made from coconut husks and is a different material, often used as a substitute for peat. It holds water in a similar way, but it is not the same product, and bale yields differ.
Can I use peat moss alone as a potting mix?
It is better mixed with other things. Straight peat dries into a crust that repels water and has few nutrients. Blend it with compost, perlite or soil, and read the mix recipe for your plants.
How deep should I work it into a bed?
A 2 to 3 inch layer worked into the top 6 to 8 inches of soil is a common amendment. The calculator's depth is the thickness of the layer you spread, before you dig it in.
Estimates only. Verify quantities with your supplier before purchasing.