Shape formulas
Round pots use π × (diameter ÷ 2)² × height. Square pots use side × side × depth. Window boxes use length × width × depth. Tapered pots use the frustum formula with the top and bottom diameters.
Pots, planters & window boxes
Potting Soil Calculator
Measure your containers. Get volume and whole bags. Add inside dimensions and quantity for round, square, rectangular or tapered pots. Compare bag sizes; add your own density and prices if needed.
Four container shapesTwo bag-size systemsRows show the largest shareNo login or usage limit
01 Measure inside02 Add rows03 Check the order
1 cu ft ≈ 25.7 dry qt · 1 L = 1,000 cm³ · 1 yd³ = 27 cu ft
Transparent container math
How this potting soil calculator works
Measure the usable inside dimensions, choose a shape and enter how many containers share that specification. The page calculates each row, adds the rows, then applies waste and settling allowances in sequence. A row marked “largest share” shows which specification is driving the total.
Use product facts
Bag volume, density and prices vary by product. Enter the printed label or supplier quote when you need bags, pounds, tons or cost.
Keep the fill level visible
Enter the height or depth you actually plan to fill, not an outside pot height. This geometric estimate does not subtract rim space, an existing root ball or other contents.
Buying with the result
From container measurements to bags
The page shows cubic feet, cubic yards, liters, dry quarts and gallons. Dry-quart bags use the displayed approximate conversion of 25.7 dry quarts per cubic foot; cubic-foot bags use their printed volume directly. Every bag count rounds up because partial bags cannot be purchased as a whole bag.
Check an order: Two rectangular planters, each 2 ft long × 1 ft wide with a 12 in planned fill depth, need 4 cubic feet before allowances. At 1.5 cubic feet per bag, that is 3 whole bags. These are editable example measurements, not recommended pot sizes or fill depths.
Common questions
Potting soil calculator FAQ
How do I calculate potting soil volume?
Measure the usable inside dimensions, choose the matching shape, enter quantity and let the page apply the displayed formula. Rows are added before allowances.
Should I use inside or outside dimensions?
Use inside dimensions because the potting mix occupies the inside space. Outside dimensions include the container wall and can overstate the amount.
How many bags of potting soil do I need?
Divide the planned volume by the printed volume of one bag and round up. This page checks 8, 16, 20 and 32 dry-quart bags plus 0.75, 1, 1.5 and 2 cubic-foot bags.
How do dry quarts and cubic feet convert?
This page uses 1 cubic foot ≈ 25.7 US dry quarts, rounded from the NIST conversion of 25.71405. Dry quarts and liquid quarts are different units. Check which unit is printed on your bag.
How do I compare bagged and bulk potting soil?
Enter your own bag price, bulk price per cubic yard and delivery or pickup fee. The calculator keeps delivery separate and never invents a local price.
Do I need to log in or register?
No. The calculator is free, has no usage limit and runs in your browser without an account.
Is this also a potting mix, planter soil or container soil calculator?
Yes. The geometry is the same for potting mix, planter soil and container soil; choose the container shape and use the volume printed on the product you plan to buy.
How much potting soil do I need for several planters?
Add one row for each specification and enter its quantity. The row totals make it clear which group of planters contributes the largest share.
Continue the project
Move from containers to the rest of the job
Measure beds with the soil calculator, compare raised-bed orders with the raised bed soil calculator, or return to the landscape material calculator for mulch and other outdoor materials.