Potting Soil Calculator
Liters and bags of potting mix for any number of pots.
Use ToolFree calculator
Pot & Container Volume Calculator
How much soil a pot holds in gallons and liters, and how many containers one bag or yard fills.
Pot & Container Volume Calculator
Chlorova · updated for 2026
Calculator
Quick samples
Click “Calculate” to see your results.
Pot volume here is the bare geometric space inside the rim, so the soil you can actually plant into is less once drainage rock, a core and the watered-in settle are accounted for. Round pots are treated as true cylinders and squares as full boxes, while tapered nursery pots narrow at the base and hold noticeably less than a straight-walled figure suggests. Round your bag count up when buying, since a bag that exactly matches the arithmetic leaves no room for spillage and a pot you under-fill will dry out far faster than the label volume implies.
Buying potting soil by guesswork means either a half-empty bag or a pot you cannot finish filling, and neither shows up until you are at the register. This pot and container volume calculator turns a pot's width and depth into the soil it holds in gallons, cubic feet and liters, then tells you how many of that pot a full cubic yard of mix fills. Pick round or square, enter the size, and you know the volume before you buy a single bag.
Finding a Pot's Soil Volume
- Choose round for a pot or square for a box or grow bag.
- Enter the diameter for a round pot or the side for a square one.
- Enter the inside depth of the pot, from rim to floor, in inches.
- Read the soil volume shown in gallons, cubic feet and liters.
- Check how many of this pot one cubic yard of mix fills.
- Add roughly ten percent extra mix for settle and drainage when buying.
- Round the bag count up so a big job never runs short.
How the Volume Is Worked Out
The soil space is the footprint times the depth, so a round pot uses the circle of its diameter and a square one uses the full width squared, all in cubic inches. Converting is plain division: 231 cubic inches make a gallon, 1,728 make a cubic foot, and multiplying by point zero one six three eight seven turns cubic inches into liters. The pots-per-yard figure divides twenty-seven cubic feet by one pot's cubic feet and rounds down, since a partial pot cannot be finished from scraps.
The shape picker only changes the footprint factor, about point seven eight five for a circle and one for a square, which is why a round and a square pot of the same width differ by nearly a quarter in soil volume. Tapered pots hold less than the straight-wall figure, so treat the answer as a rim-full maximum, not the planted volume. When you buy, lean on the cubic-foot and pots-per-yard numbers, since bagged mix is sold by the cubic foot, where arithmetic meets the shelf.
Worked Example: A Dozen 12-Inch Pots
- You are potting up twelve round nursery pots, each about 12 inches wide.
- Each pot is about 12 inches deep from its rim down to the drain hole.
- A circle of a 12-inch diameter times depth is roughly 1,358 cubic inches.
- Divided by 231 cubic inches, that is roughly 5.88 gallons of soil per pot.
- In cubic feet, each pot holds close to 0.79 cu ft of dry mix.
- So one full cubic yard therefore fills floor(27 ÷ 0.79) = about 34 pots.
- Your twelve pots fit comfortably inside a single bulk cubic-yard bag.
- Order one yard plus a small bag to cover settling and unavoidable spillage.
Common Pot Sizes and Soil Volume
Round-pot volumes at a depth equal to their width, with the pots one cubic yard of mix will fill. Change the depth in the calculator and the volume scales with it, since these are the same cylinder formula at a few familiar diameters.
| Round pot | Soil volume | Pots per cu yd |
|---|---|---|
| 6-inch starter | 0.73 gal | 275 |
| 12-inch pot | 5.88 gal | 34 |
| 16-inch pot | 13.9 gal | 14 |
| 24-inch half-barrel | 47.0 gal | 4 |
Key Terms
- Cubic inch
- The raw volume a pot holds, before it is converted into gallons, cubic feet or liters.
- Cubic foot
- The unit bagged potting mix is sold by, equal to 1,728 cubic inches.
- Cubic yard
- Twenty-seven cubic feet, the bulk volume a large bag or delivery of soil represents.
- Tapered pot
- A nursery pot narrower at the base than the rim, holding less than a straight-wall cylinder.
- Settle
- The drop in a pot's filled volume once dry mix is watered in and compacts around the roots.
Buying Soil That Actually Matches the Pots
- Buy by cubic feet, not by a remembered gallon figure, because bagged mix is labeled in cubic feet and matching units is where a shopping list goes wrong.
- Dry coir and peat mix can double in volume once wetted, so a pot packed with dry mix will settle below the rim after the first soak and need a top-up.
- A tapered pot's true volume is closer to a mid-height diameter than the rim width, so the calculator's straight-wall answer reads a little high on nursery stock.
- Under-filled pots dry out fast because there is less soil to hold water, so it is worth the extra quarter bag to fill to the correct line rather than shy of it.
- For a whole patio of the same pot, use the pots-per-yard figure as your ordering unit, since one bulk yard beats hauling and opening a dozen small bags.
Common Mistakes & Fixes
- Measuring the outside rim instead of the inside, so a wall thick enough to matter quietly shrinks the real volume.
- Treating a tapered pot as a straight cylinder and buying a yard that leaves half the pots under-filled.
- Packing dry mix to the rim and skipping the water-in, then watching the level drop a third overnight.
- Confusing a nursery pot's labeled gallons with its soil volume, when the label number is often generous.
- Buying exact-match soil with no cushion, so the last pot and every spill have nothing left to fill them.
When to Use This (and When Not To)
Use it any time you are sizing pots and need the soil volume behind them, whether matching plants to containers or ordering just enough mix for a batch. It answers one pot's volume and the yard it fills, not a raised bed's area, so size beds with the raised bed or potting soil calculator and compare bulk versus bag pricing with the material calculator. For very oddly shaped or tapered planters, treat the straight-wall figure as an upper bound and measure the real fill by bucket.
Pot & Container Volume Calculator: Frequently Asked Questions
How much soil does a 12-inch pot hold?
A round pot twelve inches wide and twelve deep holds about 5.9 gallons, or roughly 0.79 cubic feet, when filled to the rim. A tapered nursery pot of the same labeled size usually holds a bit less, so order for the straight-wall figure and expect some cushion.
How many bags of potting soil do I need?
Divide the pot's cubic feet into the bag size, then round up, since a bag that only just matches leaves nothing for spillage. A two-cubic-foot bag fills about two and a half standard 12-inch pots, while a full cubic yard does the bulk of a small patio in one delivery.
Why does a square pot hold more than a round one?
Because a square fills its whole footprint while a round pot only fills a circle inside the same width, and a circle is about three-quarters of the box around it. The shape factor in this calculator captures exactly that gap between the two.
Should I account for drainage material?
Yes, though the tool measures the full internal volume, not the planted portion. If you use a layer of perlite or rock at the base, subtract that depth from the pot's depth before calculating so the soil figure reflects what the roots actually occupy.
Is a gallon of soil a gallon of water?
By volume yes, since both use the same 231-cubic-inch gallon, but not by weight, because dry mix is far lighter than water. That is why buying by the labeled cubic feet is safer than eyeballing a gallon equivalence off a water jug.
Do grow bags match these numbers?
Closely for square fabric grow bags, since they hold a full box volume rather than a circle. Fill them a touch high anyway, because loose mix in a soft bag settles more visibly than in a rigid pot after the first watering.
Sources & Further Reading
- Container Size and Potting Mix Volume for Home Growers — University of Vermont Extension. Basis for the pot volume and pots-per-yard conversions used here.
- Watering, Settling and Aeration in Container Media — Michigan State University Extension. Underpins the settle, dry-mix and under-fill cautions on this page.
- Sizing Containers for Vegetables and Ornamentals — Clemson Cooperative Extension. Source of the common-pot reference volumes in this calculator.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
More popular tools
All toolsNew Popular Raised Bed Soil Calculator
Find the exact cubic feet of soil mix your bed needs.
Use ToolNew Bulk vs Bagged Material Calculator
Compare the real cost of buying compost, mulch or soil by the bag versus a delivered bulk yard.
Use ToolNew Pot Drainage and Watering Frequency Calculator
Size the drainage holes a pot needs and work out the watering interval, weekly gallons and soak depth for a plant and pot material.
Use Tool