Potting Soil Calculator
Find out exactly how much potting soil you need for your containers. No more buying too much or too little!
Calculation:
1. Radius = 12 ÷ 2 = 6"
2. Volume = π × 6² × 10 = 1,130 cu in
3. 90% fill = 1,017 cu in
4. Convert to cu ft: 1,017 ÷ 1,728 = 0.59 cu ft
5. Convert to gallons: 0.59 × 7.48 = 4.4 gal
Result: Need about 0.6 cu ft or 4.4 gallons of soil.
How much potting soil do I need for a container?
A good rule is to fill the container so the soil is 1-2 inches below the rim. For calculations, fill to 2 inches from top. A 12" pot needs about 3 gallons (0.4 cubic feet), a 16" pot needs about 5 gallons (0.7 cubic feet), and a 20" pot needs about 7 gallons (0.9 cubic feet).
What is the difference between potting mix and garden soil?
Potting mix is soilless, made from peat moss, perlite, and vermiculite. It is lightweight, sterile, and drains well - perfect for containers. Garden soil is heavier, may contain pathogens, and is better for in-ground planting. Never use garden soil in containers.
How many cubic feet of potting soil are in a bag?
Standard bag sizes: 1 cubic foot bags (most common), 2 cubic foot bags, and 20-quart bags (about 0.67 cubic feet). One cubic foot fills roughly: 4-5 medium pots (10-12"), 2 large pots (16"), or 8-10 small pots (6-8").
Do I need to add anything to potting soil?
Most potting mixes come with slow-release fertilizer already included. For additional nutrition, you can mix in compost (10-20%), perlite for extra drainage, or moisture-retaining crystals. Avoid adding garden soil or sand, which can compact and reduce drainage.
🔗 Related Calculators
📐 Formula
📝 Example Calculation
Calculation:
1. Radius = 12 ÷ 2 = 6"
2. Volume = π × 6² × 10 = 1,130 cu in
3. 90% fill = 1,017 cu in
4. Convert to cu ft: 1,017 ÷ 1,728 = 0.59 cu ft
5. Convert to gallons: 0.59 × 7.48 = 4.4 gal
Result: Need about 0.6 cu ft or 4.4 gallons of soil.