Compost Calculator — Cubic Yards for Garden Beds
Calculate how much compost you need in cubic yards, bags, and weight for raised beds and gardens. See also Soil Calculator and Mulch Calculator.
Bed Dimensions
How to Calculate Compost Needed
1. Measure the length and width of your garden bed in feet. 2. Decide on the depth of compost to apply (typically 2-4 inches for top-dressing). 3. Multiply length x width x (depth in inches / 12) to get cubic feet. 4. Divide by 27 to convert to cubic yards. 5. For bags, the cubic feet value equals the number of 1 cu ft bags needed.
Compost Volume Formula
Volume (cu ft) = Length (ft) x Width (ft) x Depth (in) / 12
Cubic Yards = Volume (cu ft) / 27
Bags (1 cu ft) = Volume (cu ft) rounded up
Weight (lbs) = Cubic Yards x Density (lb/yd3)
Densities:
Garden Compost: 1,000 lb/yd3
Mushroom: 900 lb/yd3
Manure-Based: 1,100 lb/yd3
Leaf Mold: 800 lb/yd3
Example
Calculate compost for a 4 ft x 8 ft raised bed at 3 inches deep:
Volume = 4 x 8 x (3/12) = 8 cu ft
Cubic Yards = 8 / 27 = 0.30 yd3
Bags (1 cu ft) = 8 bags
Weight = 0.30 x 1000 = 296 lbs
Compost Needed by Bed Size
| Bed Size | 2" Deep (yd3) | 3" Deep (yd3) | 4" Deep (yd3) |
|---|---|---|---|
| 4 x 4 ft | 0.10 | 0.15 | 0.20 |
| 4 x 8 ft | 0.20 | 0.30 | 0.40 |
| 6 x 8 ft | 0.30 | 0.44 | 0.59 |
| 8 x 10 ft | 0.49 | 0.74 | 0.99 |
| 10 x 12 ft | 0.74 | 1.11 | 1.48 |
Frequently Asked Questions
How deep should compost be for garden beds?
Apply 2-4 inches of compost for existing beds as a top-dressing. For new raised beds, mix 4-6 inches of compost into the top 8-12 inches of soil for best results.
How much does a cubic yard of compost weigh?
Compost weighs 800-1,100 pounds per cubic yard depending on type and moisture content. Wet compost is significantly heavier than dry compost.
What is the best type of compost for vegetable gardens?
Garden compost or well-aged manure-based compost works best for vegetables. Mushroom compost is slightly alkaline and good for most plants but avoid it for acid-loving plants like blueberries.
How often should I add compost to my garden?
Add 1-2 inches of compost annually in spring or fall. Heavy-feeding crops like tomatoes benefit from an additional mid-season application of 1 inch around the base.
Can I use too much compost?
Yes. Excessive compost (over 25-30% of soil volume) can cause nutrient imbalances, particularly excess phosphorus. Stick to 2-4 inches per year for established beds.