Peat Moss Calculator
Find how many compressed bales of peat moss you need to amend a garden bed at your depth, plus total cost per bale.
How this calculator works
Peat moss is sold in compressed bales that expand once opened and moistened. This calculator converts your bed’s area and depth into cubic yards, then divides by the expanded bale yield of 6 cubic feet to give you a bale (bag) count.
Formula: Cubic yards = (Length ft × Width ft × Depth ft) ÷ 27. Bales = (Cubic yards × 27) ÷ 6.
Worked example
A 10 ft × 10 ft bed at a 2-inch amendment depth:
- Depth in feet: 2 ÷ 12 ≈ 0.1667 ft
- Cubic yards: (10 × 10 × 0.1667) ÷ 27 ≈ 0.6173 yd³
- Bales: (0.6173 × 27) ÷ 6 ≈ 2.78 bags
- At $12/bale, that’s $33.33.
Coverage reference
| Bed area | Bales needed (2 in) |
|---|---|
| 5 × 5 ft | 0.69 bags |
| 10 × 10 ft | 2.78 bags |
| 20 × 20 ft | 11.11 bags |
How to measure your beds
Measure each bed’s length and width at ground level, and use a 2-3 inch amendment depth if you’re mixing peat moss into existing soil rather than building a bed from scratch. Fluff and moisten a sample bale before you rely on its expanded volume, since a compressed bale looks much smaller than what it actually yields once opened.
Frequently asked questions
What is peat moss and where does it come from?
Peat moss is partially decomposed sphagnum moss harvested from peat bogs, mostly in Canada, and sold compressed for gardening use. It's valued for its ability to hold many times its weight in water while still allowing air to reach roots.
Why does a compressed bale expand so much once opened?
A typical 3 cubic foot compressed bale expands to roughly 6 cubic feet once broken up and moistened — this calculator's bag count is based on that expanded volume, not the compressed size printed on the bale's label. Always fluff and wet peat moss before measuring how far it will actually go.
Does peat moss change soil pH?
Yes — peat moss is naturally acidic and will gradually lower soil pH, which makes it useful around acid-loving plants like blueberries, azaleas, and rhododendrons. For most vegetable beds, it's best mixed with other amendments rather than used as the dominant ingredient, since it can push pH lower than many crops prefer.
Is peat moss the same as coco coir?
No — they serve similar structural and moisture-holding roles, but coco coir is made from coconut husk fiber, is pH-neutral rather than acidic, and is generally considered the more renewable of the two since peat bogs take centuries to regenerate. Some gardeners substitute coir for peat moss for that sustainability reason.
Can I use peat moss alone as a potting mix?
No — peat moss holds moisture and improves structure, but it has essentially no nutrient content on its own. It works best blended with compost, perlite, or a commercial potting mix rather than used by itself to fill a container or bed.
Estimates only. Verify quantities with your supplier before purchasing.