Garden calculator
Compost Calculator
Estimate compost in cubic yards, complete bags, and bulk increments, with a side-by-side purchase cost.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
Calculate the quantity for a specified surface layer or measured fill. The tool does not determine how much compost the soil needs; that decision depends on soil conditions, the compost, and the intended planting. Enter bag volume from the package and bulk increments from the supplier. The calculator applies one visible purchase allowance and reports both supply methods as alternatives.
Layer ft³ = length × width × depth in inches ÷ 12. Adjusted ft³ = layer ft³ × (1 + allowance ÷ 100). Bags = round up(adjusted ft³ ÷ bag ft³). Bulk order = adjusted yd³ rounded to the selected increment.
Worked example
A realistic starting point
At 20 × 10 ft and 1 inches, the measured layer is 16.67 ft³. With a 10% allowance it becomes 18.33 ft³, requiring 10 complete 2 ft³ bags. Bulk delivery is rounded separately to your selected increment.
What changes the answer
Factors worth checking
New material depth
Measure the layer being added. Including both existing material and the full desired finished depth overstates the new purchase.
Bag volume and delivery
A bag’s weight is not a substitute for its volume. Compare the stated cubic feet with bulk cubic yards, and add delivery only to the option that incurs it.
Allowance versus application
The purchase allowance helps cover quantity uncertainty. It does not instruct you to apply a thicker layer everywhere. Keep any excess for an appropriate later use.
Common questions
Compost FAQ
Can I fill a raised bed entirely with compost?
The volume calculation does not recommend a soil blend. Choose a suitable growing medium using soil or horticultural guidance, then calculate the volume of each component separately.
Why are bagged and bulk quantities different?
Each method rounds to different package increments. The underlying adjusted volume is the same, but purchased volume can exceed it by different amounts.
Can I price several bag sizes?
Change bag volume and price in the comparison scenario. Compare final costs and purchased volumes, not just the sticker price of one bag.
Evidence
Sources & review
- University of Minnesota Extension — soil testingSoil and nutrient needs should be assessed before choosing amendments.
- NIST — SI units: volumeUnit relationships; supplier product coverage and prices remain separate inputs.
Published by Calcstead. Report a correction.
Method and source links reviewed September 6, 2026. Price presets are editable planning inputs and should be replaced with current local information.