Potting Soil Calculator
Estimate potting mix for round planters and containers. Enter the inside diameter, soil fill depth and number of similar pots to estimate cubic feet, gallons and bag quantities.
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Planning estimate only. Confirm local prices, supplier specifications and site conditions before ordering.
Your estimate
Round containers are approximated as cylinders. Tapered pots, root balls and watering space usually reduce the actual amount of potting mix used.
How the potting soil calculator works
For a round container, volume = π × radius² × fill depth. Inch measurements are converted to feet, then the total is multiplied by the container count and allowance.
For a better estimate
- Use inside container dimensions where possible.
- Leave room below the rim for watering rather than calculating to the absolute top edge.
- Tapered planters need less soil than a perfect cylinder, so this calculator is intentionally conservative for strongly tapered pots.
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Frequently asked questions
How much potting soil do I need for a pot?+
For a round pot, estimate the inside container as a cylinder using its diameter and fill depth. Tapered pots will use somewhat less.
How many gallons are in a cubic foot of potting soil?+
One cubic foot is about 7.48 US gallons by volume.
Why should I not fill to the very top?+
Most containers need watering space below the rim, and plants or root balls also displace some potting mix.