Buying soil for a raised bed or a row of planters and staring at bags labeled “8 quarts” and “1.5 cubic feet” is a fast way to end up with a trunk full of extra bags you didn’t need. The math trips up most gardeners on the first trip, because there are two different “quarts” in the U.S. measurement system — and only one of them is used for soil. Get the wrong number, and you either buy 16% too much or run short mid-project. Here’s the conversion that works every time, the bag sizes you’ll actually see in stores, and the common mistakes that waste your money.
25.7 Dry Quarts Per Cubic Foot — The Garden Number
The conversion you need for any soil, compost, or mulch project is 25.71 dry quarts per cubic foot, almost always rounded to 25.7 qt on calculators and garden charts. This uses the U.S. dry quart, which measures 67.2 cubic inches — the standard the entire bagged-soil industry follows. The liquid quart, at 57.75 cubic inches, gives you 29.92 quarts per cubic foot and is only correct for water, milk, and pesticides. Using the liquid number on soil overestimates your needs by about 16%.
Bag Sizes You’ll Find in Stores Today
Soil bags at Home Depot, Lowe’s, Costco, and Sam’s Club come in a handful of standard sizes. Some brands label by quarts, others by cubic feet — knowing which is which saves the arithmetic at the shelf. The table below shows the current 2024–2026 retail standards.
| Bag Label | Actual Volume (Dry Quarts) | Actual Volume (Cubic Feet) |
|---|---|---|
| 8 Quart | 8 qt | 0.25 ft³ |
| 20 Quart | 20 qt | ~0.78 ft³ |
| 1 Cubic Foot | ~25.7 qt | 1.0 ft³ |
| 1.5 Cubic Foot | ~38.5 qt | 1.5 ft³ |
| 2 Cubic Foot | ~51.4 qt | 2.0 ft³ |
| 40 Quart | 40 qt | ~1.55 ft³ |
| 40 lb Topsoil | Varies by density | ~0.75 ft³ |
Notice the 40-quart bag and the 1.5-cubic-foot bag are nearly the same volume — that’s the size that often confuses shoppers comparing Miracle-Gro at Sam’s Club against generic topsoil at the hardware store. If you’re deciding which bag to grab for a medium project, our tested roundup of the best 1.5 cubic feet soil options breaks down weight, quality, and value for raised beds and large containers.
How To Do The Conversion Yourself
If your planter doesn’t match a standard bag size, the math is straightforward. Start with your container’s dimensions in inches: Length × Width × Height gives you cubic inches. For a 24″ × 12″ × 12″ raised bed, that’s 3,456 in³. Divide by 67.2 (the number of cubic inches in one dry quart), and you get 51.4 dry quarts — almost exactly two cubic feet. The direct formula is: cubic feet × 25.714 = dry quarts. Multiply your per-planter total by the number of pots, and you have your shopping list.
Three Mistakes That Waste Soil and Money
The first error is mixing up liquid and dry quarts — a 16% overbuy on a large project can mean two extra bags you’ll never use. The second is assuming weight equals volume. A 40-pound bag of topsoil packs into about 0.75 cubic feet, while a 40-pound bag of lighter potting mix can fill nearly twice that space. The third is forgetting that a cubic yard, used for bulk deliveries, holds 27 cubic feet — roughly 694 dry quarts. Rounding errors are also common: a 1.5 cubic foot bag is 38.5 quarts, not 38, and the difference adds up across six raised beds.
Why Moisture Content Changes Everything
A bag of soil straight off the pallet weighs more than the same volume of dry mix from the back of the shed, because moisture adds weight without changing volume. Topsoil at field moisture runs about 40 pounds per cubic foot. Potting mix, with more peat and perlite, is lighter. The volume number stays the same — 25.7 dry quarts per cubic foot — but the physical weight your car carries and your back lifts can vary by 20% or more. For big projects, a dolly or a second pair of hands saves a lot of trouble, because a 2-cubic-foot bag can hit 50 pounds when it’s wet.
| Container Type | Typical Volume (Dry Quarts) | Bags Needed (1.5 ft³ bags) |
|---|---|---|
| Standard 10″ pot | ~3.5 qt | 1 bag fills ~11 pots |
| Large 14″ planter | ~8 qt | 1 bag fills ~5 planters |
| 3×3 raised bed (12″ deep) | ~96 qt | ~2.5 bags |
| 4×4 raised bed (12″ deep) | ~171 qt | ~4.5 bags |
Quarts Per Cubic Foot — The Final Conversion Reference
Keep these numbers handy for your next trip to the garden center: 1 cubic foot always equals 25.7 dry quarts for any soil, compost, or mulch. A 1.5 cubic foot bag holds 38.5 quarts, a 2 cubic foot bag holds 51.4 quarts, and a 40-quart bag is about 1.55 cubic feet. Measure your planter’s length, width, and depth in inches, multiply them together, divide by 67.2, and you’ll walk out of the store with exactly what you need — and no extra bags to return.
FAQs
Do all soil brands use the same quart measurement?
Yes — every bagged soil, topsoil, and compost brand sold at US hardware and garden retailers uses the U.S. dry quart. Miracle-Gro, Scott’s, Kellogg, and generic store brands all follow the 25.7 quarts per cubic foot standard.
Why does a 40-pound bag hold less than a 40-quart bag?
Pounds measure weight; quarts measure volume. Potting mix is lighter than topsoil, so a 40-pound bag of potting mix may hold more cubic footage than a 40-pound bag of topsoil. Always check the volume in quarts or cubic feet, not the weight.
Can I use liquid quart measurements for garden soil?
No. Liquid quarts give you 29.92 per cubic foot, which overestimates soil volume by about 16%. That error leads to buying too much soil and wasting money. Stick with the dry quart conversion for all gardening materials.
How much area does a 2 cubic foot bag cover?
A 2 cubic foot bag (about 51.4 dry quarts) fills one 4×2 raised bed at 3 inches deep, or about eight 12-inch diameter pots. Coverage depends on your container’s depth — shallower beds stretch the bag further.
References & Sources
- GoCalc. “Potting Soil Calculator.” Provides the standard 25.7 dry quarts per cubic foot conversion and current bag-size table.