How Many Bags of Potting Soil Do I Need?
Wondering how many bags of potting soil do I need for your planters? Enter the number of pots and their size โ either by volume in gallons or by diameter and height โ and this free potting soil bag calculator tells you the total gallons, total cubic feet, and how many bags of your chosen bag size to buy. Results update instantly as you type.
Enter your numbers
Your results
| Total soil (gallons) | โ |
| Total soil (cubic feet) | โ |
| Selected bag size | โ |
| Bags to buy (rounded up) | โ |
Estimated amount: bags round up to the next whole bag since you can't buy part of a bag. Soil settles 10โ15% after watering, so fill pots generously and top up before planting.
How to use this calculator
Enter the number of pots you need to fill. Then pick a sizing method: if you know each pot's capacity in gallons, choose "By volume"; if not, choose "By diameter ร height" and measure the top diameter and height in inches โ the calculator treats the pot as a cylinder and converts to gallons automatically.
Set the fill level (90% by default) to leave headroom for watering, then pick the bag size your store sells โ 1, 1.5, 2, or 2.5 cubic feet. Results update instantly: you'll see the total soil in gallons and cubic feet plus the number of bags to buy, rounded up to the next whole bag.
Buy the rounded-up bag count. Leftover potting soil keeps indefinitely if stored dry in a sealed bag or bin.
How it works
The calculator converts everything to gallons, then to cubic feet, using two constants: 1 cubic foot = 7.48052 gallons and 231 cubic inches = 1 gallon. In volume mode: total gallons = pots ร gallons per pot ร fill level. In dimensions mode: per-pot gallons = ฯ ร (diameter รท 2)ยฒ ร height รท 231, then multiplied by pots and fill level.
Next, total cubic feet = total gallons รท 7.48052. The bag count rounds up to the next whole bag: bags = ceil(total cu ft รท bag size). Example: 10 pots ร 2 gallons = 20 gallons รท 7.48052 = 2.674 cu ft; with 2 cu ft bags that's 1.34 bags โ 2 bags. These are estimates: real pots are often slightly tapered (not perfect cylinders) and soil settles after watering, so the fill percentage and rounding up cover that slack.
Frequently asked questions
How many bags of potting soil do I need for one pot?
It depends on the pot's volume and the bag size. A typical 5-gallon nursery pot holds about 5 gallons of soil, and 1 cubic foot of potting soil is about 7.48 gallons, so one 2 cu ft bag fills roughly three 5-gallon pots. Enter your pot count, pot size, and bag size above and the calculator works out the exact number of bags for your project.
How many gallons are in a cubic foot of potting soil?
One cubic foot equals 7.48052 gallons, which this calculator rounds to 7.48 gallons. So a 1 cu ft bag of potting soil fills about 7.5 gallons of pot space, a 1.5 cu ft bag about 11.2 gallons, and a 2 cu ft bag about 15 gallons. These are exact volume conversions, so the soil weight or brand does not change the number.
Should I fill my pots all the way to the top with soil?
No. Leave about 1 inch of headroom between the soil surface and the pot rim so water soaks in instead of running off. This calculator defaults to a 90% fill level for exactly this reason. You can raise it to 100% if you like to top pots right up, or lower it if you fill pots only partway.
Does potting soil settle after watering?
Yes. Fresh potting soil typically settles 10-15% after the first few waterings as air pockets collapse and the mix compacts. Fill pots generously, water them in, then top up with fresh mix before planting if the level has dropped. The calculator's fill percentage gives you a practical number of bags that accounts for this.
Can I reuse potting soil from last year?
Yes. Used potting soil can be reused for a season or two if you refresh it: pick out old roots and debris, mix in about 25-30% fresh compost, and add a balanced slow-release fertilizer since old mix is usually depleted of nutrients. If last year's plants had soil-borne diseases, replace the mix instead of reusing it.