Compost Calculator
Compute compost using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
Volume (cu yd) = (Length x Width x Depth in inches / 12) / 27
Multiply garden length by width to get area in square feet, multiply by depth converted from inches to feet (divide by 12) to get volume in cubic feet, then divide by 27 to convert to cubic yards (the standard bulk compost measurement). Weight is estimated by multiplying cubic yards by compost density (typically 800-1,000 lbs per cubic yard).
Worked Examples
Example 1: New Vegetable Garden Bed
Problem: A 20 x 10 foot vegetable garden needs 3 inches of compost worked into the soil. Bulk compost costs $35/cubic yard.
Solution: Area: 20 x 10 = 200 sq ft\nDepth in feet: 3/12 = 0.25 ft\nVolume: 200 x 0.25 = 50 cu ft\nCubic yards: 50/27 = 1.85 cu yards\nWeight (at 900 lbs/cu yd): 1.85 x 900 = 1,667 lbs\nCost: 1.85 x $35 = $64.81
Result: Need 1.85 cubic yards (50 cu ft) | Weight: 1,667 lbs | Cost: $64.81
Example 2: Lawn Topdressing
Problem: A 5,000 sq ft lawn needs 0.5 inches of compost topdressing. Compost is $40/cubic yard.
Solution: Area: 5,000 sq ft\nDepth in feet: 0.5/12 = 0.0417 ft\nVolume: 5,000 x 0.0417 = 208.3 cu ft\nCubic yards: 208.3/27 = 7.72 cu yards\nWeight: 7.72 x 900 = 6,944 lbs (3.47 tons)\nCost: 7.72 x $40 = $308.64
Result: Need 7.72 cubic yards (208 cu ft) | Weight: 3.47 tons | Cost: $308.64
Frequently Asked Questions
How much compost do I need for my garden?
The amount of compost needed depends on your garden area and the desired application depth. For general garden beds, a 2-3 inch layer is standard for soil amendment. For new gardens or poor soils, use 3-4 inches. For topdressing established beds, 1-2 inches is sufficient. To calculate, multiply your garden length by width to get square footage, multiply by the depth in feet (inches divided by 12), then divide by 27 to convert cubic feet to cubic yards. One cubic yard of compost covers about 108 square feet at 3 inches deep.
What are the different types of compost and when should I use each?
General purpose compost is a balanced mix suitable for most garden applications. Mushroom compost is alkaline and nutrient-rich, ideal for vegetable gardens but not acid-loving plants like blueberries. Composted manure (cow, horse, or chicken) is high in nitrogen and excellent for heavy feeders like tomatoes and corn. Leaf mold compost is lower in nutrients but excellent for improving soil structure and moisture retention. Vermicompost (worm castings) is the most nutrient-dense option, best used as a concentrated amendment mixed at 10-20% into potting soil or applied as a thin top dressing.
How much does compost cost and is bulk or bagged cheaper?
Bulk compost typically costs $25-$50 per cubic yard, while bagged compost costs $5-$10 per cubic foot (equivalent to $135-$270 per cubic yard). Bulk is significantly cheaper for large projects. A cubic yard equals 27 cubic feet or about 13-14 two-cubic-foot bags. For areas under 100 square feet, bagged may be more practical despite the higher per-unit cost. Many municipalities offer free or low-cost compost from yard waste recycling programs. Delivery fees for bulk compost typically range from $30-$75 depending on distance.
How deep should I apply compost to my garden?
Application depth depends on your goal. For annual topdressing of established gardens, apply 1-2 inches in spring. For new garden bed preparation, work 3-4 inches into the top 6-8 inches of existing soil. For lawn topdressing, apply only 0.25-0.5 inches. For raised beds being filled for the first time, compost should make up about 30-40% of the total fill mix. When amending clay soil, use 3-4 inches worked deeply into the soil. Sandy soils also benefit from 3-4 inches to improve water retention. Over-applying compost can create nutrient imbalances, particularly excess phosphorus.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Does Compost Calculator work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.