Guide
How Much Garden Soil Do I Need? (Formula + Chart)
Multiply square feet by depth in inches, divide by 324 for cubic yards. Plus a coverage chart, bag counts, and a direct answer for square-foot gardens.
The short answer
Multiply square feet by depth in inches, then divide by 324 for cubic yards. A 4 × 8 ft bed (32 sq ft) topped 3 inches deep needs 32 × 3 ÷ 324 = about 0.3 cubic yards, which is 8 cubic feet, or roughly 5 to 6 bags of 1.5 cubic feet. Round up.
Try it — Garden Soil Calculator
Full calculatorEnter a bulk price to estimate cost.
You need
1.85cu yd
- Cubic feet
- 50 cu ft
- Cubic yards
- 1.85 cu yd
- Bags (1.5 cu ft)
- 34 bags
- Weight
- ≈ 1.85 tons
Bulk is sold by the yard — order 2 cu yd to have enough.
Garden soil is the blended, ready-to-grow product you mix into in-ground beds. You buy it by the cubic foot in bags or by the cubic yard in bulk, but you measure your bed in square feet. Bridge that gap and the order is easy.
This guide gives you the formula, a coverage chart, real bag counts, a direct answer for square foot gardens, and the one thing the calculators skip: when garden soil is the right pick and when topsoil or a raised-bed mix belongs in the bed instead.
The formula (and the shortcut)
Garden soil volume is area times depth, with both in the same unit.
The clean path uses the shortcut: square feet × depth in inches ÷ 324 = cubic yards. That 324 is just 12 × 27. The 12 turns inches of depth into feet. The 27 turns cubic feet into cubic yards.
cubic yards = square feet × depth (inches) ÷ 324
The long way gives the same answer. Measure length, width, and depth all in feet, then divide by 27, because a cubic yard is 3 feet on each side.
cubic yards = (length_ft × width_ft × depth_ft) ÷ 27
The common trap is depth. You measure length and width in feet but depth in inches. Mixing the two is the fastest way to a wrong number.
How much soil do you need for a square foot garden?
Short answer: for an in-ground square foot bed topped 6 inches deep, plan on about 0.5 cubic feet of garden soil per square foot of bed.
That per-square-foot rate comes straight from the formula: 1 sq ft × 6 in ÷ 12 = 0.5 cu ft. Scale it to your actual bed size instead of buying "per square foot," since bags and bulk orders round to whole units anyway.
Here is that rate applied to the bed sizes square-foot gardeners actually build.
| Square foot garden size | Area | Soil at 6 in deep | Soil at 12 in deep (boxed) |
|---|---|---|---|
| 2x2 ft | 4 sq ft | 2.0 cu ft | 4.0 cu ft |
| 4x4 ft | 16 sq ft | 8.0 cu ft | 16.0 cu ft |
| 4x8 ft | 32 sq ft | 16.0 cu ft | 32.0 cu ft |
| 8x8 ft | 64 sq ft | 32.0 cu ft | 64.0 cu ft |
The standard 4x4 ft square foot garden (16 sq ft) topped 6 inches deep needs 8 cubic feet of garden soil, which is about 0.3 cubic yards, or roughly 6 bags of 1.5 cubic feet, rounding up from 5.3.
If your square foot garden is a boxed raised bed instead of an in-ground plot, fill it the fuller 10 to 12 inches most raised-bed guidance recommends, not the shallow 6 inch depth. At 12 inches, that same 4x4 box needs 16 cubic feet, double the 6 inch figure. For a boxed bed, also check the how much soil for a raised bed guide, since a deep box is usually filled with a blended mix (topsoil, compost, and aeration) rather than straight bagged garden soil.
Common mistake
Using the 6 inch, in-ground rate for a boxed raised bed. A shallow in-ground square foot garden and a 12-inch raised box are not the same job, even at the same footprint. Confirm which one you have before you order, since the box needs roughly double the soil.
A worked example and a bag count
Say you are topping a 10 × 4 ft in-ground bed with 4 inches of garden soil before planting.
cubic yards = (10 × 4) × 4 ÷ 324 = 40 × 4 ÷ 324 = 0.49 cubic yards
That is about half a yard. In cubic feet, the same job is 40 × 4 ÷ 12 = 13.3 cubic feet.
For bagged garden soil at 1.5 cubic feet per bag, that is 13.3 ÷ 1.5 = 8.9, rounded up to 9 bags. Always round up. A partial bag costs a whole bag, and a short bed means a second trip.
Coverage chart: how far one cubic yard goes
When you top a bed instead of filling a box, depth changes everything. One cubic yard is a fixed 27 cubic feet. The shallower you spread it, the more ground it covers.
These are the exact figures per cubic yard, plus how many bags make a yard.
| Depth | Coverage per cubic yard |
|---|---|
| 2 inches | 162 sq ft |
| 3 inches | 108 sq ft |
| 4 inches | 81 sq ft |
| 6 inches | 54 sq ft |
Bags to make one cubic yard depend only on bag size.
| Bag size | Bags per cubic yard |
|---|---|
| 1 cubic foot | 27 bags |
| 1.5 cubic feet | 18 bags |
| 2 cubic feet | 14 bags |
Depth, not area, is the lever. A 200 sq ft bed at 2 inches needs 200 × 2 ÷ 324 = 1.23 cubic yards. The same bed at 4 inches doubles to 2.47 cubic yards.
Grow bags: gallons to cubic feet
Fabric grow bags are sized in gallons, not cubic feet, which is its own conversion. One US gallon is about 0.1337 cubic feet.
| Grow bag size | Cubic feet (full) | Usable soil (~90%) |
|---|---|---|
| 5 gal | 0.67 cu ft | 0.6 cu ft |
| 10 gal | 1.34 cu ft | 1.2 cu ft |
| 15 gal | 2.0 cu ft | 1.8 cu ft |
| 20 gal | 2.67 cu ft | 2.4 cu ft |
| 25 gal | 3.34 cu ft | 3.0 cu ft |
| 30 gal | 4.01 cu ft | 3.6 cu ft |
Pro tip
Fill a grow bag to about 90 percent of its stated volume, not the brim. That leaves headroom for watering without soil washing over the sides, and it is why the "usable soil" column runs a bit below the raw gallon-to-cubic-foot conversion.
Garden soil vs topsoil vs raised-bed mix
You can know your cubic yards exactly and still buy the wrong bag. The three look alike on the shelf, but they are made for different jobs.
| Material | Use it for | Don't use it for |
|---|---|---|
| Garden soil | Topping up and amending in-ground beds | Filling a deep raised bed or pot on its own |
| Topsoil | Leveling, grading, building up low ground | A finished growing medium by itself |
| Raised-bed / soilless mix | Raised beds and containers | Filling a big hole on a budget |
Garden soil is topsoil blended with compost or organic matter. Per Michigan State University Extension, "landscape suppliers often blend compost or other organic matter with topsoil and sell it as garden soil." It belongs in the ground, mixed into your existing soil to top up or enrich a bed.
Topsoil is mineral soil. There is no regulated definition for the word, so quality varies, and the same MSU page warns bagged topsoil can even hide construction debris. Use topsoil to level or build up ground, then mix it into a bed rather than layering it on top, so roots do not stall at the seam.
Raised-bed or soilless mix is the lighter, better-draining medium built for tall beds and pots. For a raised bed, the University of Maryland Extension suggests filling with compost and a soilless growing mix in a 1:1 ratio rather than packing it with dense garden soil. The same extension office notes vegetables in raised beds generally want 12 to 24 inches of growing depth for deeper-rooted crops.
Pro tip
Order about 10 percent extra. Fresh garden soil settles after the first few waterings, and a bed that looked full on delivery day often sits low a week later. The bulk-vs-bagged crossover comes near one cubic yard. Above a yard, delivered bulk usually beats hauling 18 to 27 bags. Below it, bags are simpler.
Common mistake
Filling a deep raised bed with pure bagged garden soil. Alone in a tall frame it packs down and drains poorly. Maryland Extension recommends a blend instead, such as compost and a soilless mix in a 1:1 ratio. Cut garden soil with compost and a lighter medium so the roots get air and drainage.
Buying garden soil: bags vs bulk, without chasing store prices
Retail promos and per-bag pricing change constantly by store and season, so this guide will not quote a live price. What stays true regardless of the sale price is the volume math that decides bags vs bulk:
- Under about 1 cubic yard total: bags are simpler, no delivery minimum to clear
- Around 1 cubic yard: compare both — check the delivery fee against the bag count (18 to 27 bags)
- Over 1 cubic yard, or multiple beds: bulk delivery almost always wins per cubic foot
Whatever the price per bag is this week, that crossover point does not move, because it is set by delivery minimums and hauling effort, not by the sale price on the shelf.
Where to go next
For a deep frame, the raised-bed soil calculator handles the full blend. For leveling jobs, see how much topsoil do I need. For the general which-soil question and the plain volume formula, the how much soil do I need guide covers every material. Spreading a thin layer over a lawn instead of a bed is a different job. See how to top dress a lawn or run the numbers in the topdressing calculator for that thinner depth.
The math gives you a number you can trust. Got your dimensions? Open the Garden Soil Calculator and get your exact cubic yards and bag count in ten seconds, or use the Soil Calculator's cubic yards page for a broader soil mix.
Common questions
How much soil do you need for a square foot garden?
For a shallow, in-ground square foot bed topped 6 inches deep, budget about 0.5 cubic feet of garden soil per square foot (1 sq ft × 6 in ÷ 12 = 0.5 cu ft). A standard 4x4 ft square foot garden (16 sq ft) at 6 inches needs 8 cubic feet, about 0.3 cubic yards, or roughly 6 bags of 1.5 cubic feet. A boxed square-foot garden filled a full 12 inches needs double that, about 16 cubic feet.
How do I calculate how much garden soil I need?
Measure the area in square feet, pick your depth in inches, then divide by 324 for cubic yards. The long way is length × width × depth, all in feet, divided by 27. A 4 × 8 ft bed topped 3 inches deep needs 8 cubic feet, about 0.3 cubic yards. For bags, divide cubic feet by the bag size and round up.
How many bags of garden soil are in a cubic yard?
A cubic yard is 27 cubic feet. At the common 1.5 cubic feet per bag, that is 18 bags per yard. At 1 cubic foot per bag it is 27 bags. Above about a cubic yard, bulk delivery is usually cheaper than hauling 18 to 27 bags.
How far does a cubic yard of garden soil spread?
One cubic yard covers about 162 square feet at 2 inches deep, 108 square feet at 3 inches, 81 square feet at 4 inches, and 54 square feet at 6 inches. Shallower means more ground per yard. Divide 324 by your depth in inches to get coverage.
Is garden soil the same as topsoil?
No. Topsoil is mineral soil, often sold to level or build up ground. Garden soil is topsoil blended with compost or organic matter, meant to be mixed into in-ground beds. Per Michigan State University Extension, suppliers blend compost with topsoil and sell it as garden soil. Use garden soil to top up beds, not to fill a deep raised bed on its own.
How much soil for a 20 gallon grow bag?
About 2.67 cubic feet. One US gallon equals roughly 0.1337 cubic feet, so 20 gallons is 20 × 0.1337 ≈ 2.67 cubic feet. In practice, fill to about 90 percent of the bag's stated volume to leave room for watering, so plan on roughly 2.4 cubic feet of usable soil for a 20 gallon bag.
Can I fill a raised bed with just bagged garden soil?
It is not the best choice for a deep bed. Bagged garden soil packs down and drains poorly when used alone in a tall frame. The University of Maryland Extension recommends a blend, such as compost and a soilless mix in a 1:1 ratio. Mix garden soil with compost and a lighter medium instead of filling deep with it straight.
Sources
Agronomic claims in this guide are checked against these primary sources.
- The shocking truth about topsoil — Michigan State University Extension
- Soil to Fill Raised Beds — University of Maryland Extension
- Growing Vegetables in Raised Beds — University of Maryland Extension
Keep reading
How Much Soil Do I Need? (And Which Soil to Buy)
Multiply length × width × depth in feet, divide by 27 for cubic yards. Plus a which-soil chooser so you buy the right material, not just the right amount.
Read →How Much Topsoil Do I Need? (Tons, Yards + Calculator)
Topsoil is sold by the ton. Multiply your square feet by depth in inches, divide by 324 for cubic yards, then plan for about 1.2 tons per yard.
Read →How Much Soil for a Raised Bed?
Length times width times height in feet, divided by 27, gives cubic yards. A 4x8 bed at 10 inches needs about 1 cubic yard. Formula, mix ratios, bag list, and a calculator.
Read →How Much Compost Do I Need?
Multiply square feet by depth in inches, divide by 324 for cubic yards of compost. Formula, worked examples, and a bagged-vs-bulk guide.
Read →How to Top Dress a Lawn (Depth, Material + How Much)
Spread compost or topsoil over your lawn in a thin layer, 1/4 to 1/2 inch. A 1,000 sq ft lawn at 1/4 inch needs about 0.77 cubic yards.
Read →How Much Does a Yard of Topsoil Weigh?
A yard of screened topsoil weighs roughly 2,000 to 2,700 lb, about 1.0 to 1.3 tons (0.9 to 1.2 tonnes). It varies with moisture. Here is the range, a table, and the math.
Read →