Potting Soil Calculator
Enter your pots, planters or raised beds and get the potting mix needed in dry quarts, cubic feet and litres, and how many bags to buy.
Measure inside the pot. For straight-sided pots, enter the same top and bottom size. The result updates as you type.
Potting mix needed
4 bags of 16 qt
50.5 dry quarts · 1.96 cu ft · 55.6 litres
| Container 1 (× 4) | 50.5 dry qt |
What this page cannot tell you
How much the mix settles after watering, or how loosely it was packed in the bag. Fluffy mixes compress, so you may want a little extra; the page adds nothing on its own. 'Gallon' nursery pot sizes are trade names, not true volumes — measure the pot.
How to calculate potting soil
- Measure each container. Inside top and bottom size and height, in inches.
- Enter how many. Identical containers count once with a quantity.
- Set the headspace. How far below the rim you fill.
- Enter the bag size. In dry quarts, cubic feet or litres, from the bag.
- Read the amount. Dry quarts, cubic feet, litres and bags.
10 situations where a potting soil calculator helps
Spring repotting
Add up all your pots before the garden-centre trip.
Raised beds
A 4 × 8 ft bed 12 in deep takes 32 cu ft.
Patio planters
Rectangular planters by length, width and depth.
Tapered pots
Sloped sides hold less than a cylinder; the page measures the taper.
Bags labelled in quarts
Convert cubic inches to the dry quarts on the bag.
Comparing bag sizes
Change the bag size to see which is cheaper per pot.
Seed-starting trays
Small cells add up; enter the count.
Houseplant collections
List several pot sizes at once.
Nursery 'gallon' pots
Measure them — trade sizes aren't true gallons.
Metric bags
Choose litres for bags labelled that way.
How the volume is worked out
Round pots with sloped sides are a truncated cone (frustum): volume = π × h ÷ 3 × (R² + R·r + r²), where R and r are the top and bottom radii. Square pots use the square frustum h ÷ 3 × (A² + A·a + a²); planters and raised beds are length × width × height. The fill stops at your headspace, and the top size is reduced to match the fill height.
Bagged potting mix is sold by volume, often in dry quarts. A US dry quart is 67.200625 cubic inches (NIST Handbook 44, Appendix C) — larger than a liquid quart. A cubic foot is 1,728 in³ and a litre 61.024 in³.
Limits: potting mix settles after watering and is packed loosely in bags, so you may want a little extra; nothing is added automatically. Everything runs in your browser.
Sources
- NIST Handbook 44 — US dry quart = 67.200625 in³
Frequently asked questions
How much potting soil for a 12 inch pot?
It depends on depth and taper; a 12 in pot 9 in across the bottom and 11 in tall, filled to 1 in below the rim, holds about 13 dry quarts.
How many quarts are in a cubic foot?
About 25.7 dry quarts (1,728 ÷ 67.2).
How much soil for a 4 × 8 raised bed?
At 12 in deep, 32 cubic feet.
Is a dry quart the same as a liquid quart?
No: a US dry quart is 67.2 in³; a liquid quart is 57.75 in³.
How big is a 1 gallon nursery pot?
Nursery sizes are trade names and vary by maker; measure the pot.
Should I buy extra?
Mix settles, so a little extra is common; the page doesn't add any by itself.
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