Last updated: June 24, 2026
Potting Soil Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
Potting soil volume is calculated as Length × Width × Depth × Quantity ÷ 1,728, giving cubic feet from dimensions measured in inches. For example, a 48 × 24 inch raised bed filled 12 inches deep needs 8 cubic feet, or four 2-cubic-foot bags. This free calculator also reports dry quarts, cubic yards, the number of bags, and an estimated cost.
To find how much potting soil you need, multiply the length, width, and depth in inches, then divide by 1,728 to get cubic feet.
Key Takeaways
- Potting soil volume (cu ft) = Length × Width × Depth × Quantity ÷ 1,728, with dimensions in inches.
- There are 1,728 cubic inches in a cubic foot and 27 cubic feet in a cubic yard.
- One cubic foot of mix is about 25.7 dry quarts; a 2 cu ft bag is roughly 51 quarts.
- A 4×4 ft raised bed filled 12 inches deep needs about 8 cubic feet — four 2 cu ft bags.
- Buy about 10% extra to allow for settling after the first few waterings.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
Volume (cu ft) = (Length × Width × Depth × Quantity) ÷ 1728
Where:
- V=Potting soil volume(cubic feet)
- L=Container length / diameter(inches)
- W=Container width(inches)
- D=Soil depth(inches)
- Q=Number of containers(containers)
- 1728=Cubic inches per cubic foot (12³)(in³/ft³)
Worked Examples
Single patio container
A 12 × 12 inch square planter filled 10 inches deep with potting mix.
- 1Volume = 12 × 12 × 10 = 1,440 in³
- 2Cubic feet = 1,440 ÷ 1,728 = 0.83 cu ft
- 3Quarts = 0.83 × 25.71 ≈ 21.4 dry quarts
- 4Bags (2 cu ft) = ⌈0.83 ÷ 2⌉ = 1 bag
Raised bed with cost estimate
A 48 × 24 inch raised bed filled 12 inches deep, using $9.50 bags of 2 cu ft mix.
- 1Volume = 48 × 24 × 12 = 13,824 in³
- 2Cubic feet = 13,824 ÷ 1,728 = 8 cu ft
- 3Bags = ⌈8 ÷ 2⌉ = 4 bags
- 4Cost = 4 × $9.50 = $38.00
Introduction
The Potting Soil Calculator tells you exactly how much potting mix to buy for any container, raised bed, or window box. Enter the length, width, and soil depth in inches (plus how many containers you're filling), and it returns the volume in cubic feet, dry quarts, and cubic yards, the number of bags needed, and an optional cost estimate. The math is simple — volume ÷ 1,728 to convert cubic inches to cubic feet — but buying the right amount saves money and trips to the store. Planning a planting too? Pair this with our plant spacing calculator and fertilizer calculator.
How the Potting Soil Calculator Works
Potting soil is sold by volume, so you need the volume of your container, not its area. The calculator multiplies length × width × depth to get cubic inches, multiplies by the number of containers, then divides by 1,728 (the cubic inches in a cubic foot) to get cubic feet. From there it converts to dry quarts and cubic yards and divides by your bag size to find how many bags to buy, rounding up.
Enter length, width, and soil depth in inches
Add how many identical containers you're filling
Choose your bag size in cubic feet (1, 1.5, or 2 are common)
Optionally enter price per bag for a cost estimate
Read volume in cubic feet, quarts, and the number of bags
Fill containers to about 1–2 inches below the rim so water doesn't spill over — use that filled depth, not the full container height.
Round Pots and Other Shapes
For a round pot, the rectangle formula slightly overestimates because a circle fills about 79% of its bounding square. A quick fix is to enter the pot's diameter for both length and width — you'll buy a little extra, which is usually fine. For a precise figure, use the cylinder volume π × r² × depth. Tapered (flared) pots hold less than straight-sided ones of the same rim size, so round down a touch for those.
| Container Shape | How to Enter It | Note |
|---|---|---|
| Square / rectangular | Length × width × depth | Exact |
| Round (straight-sided) | Diameter for L and W | ~21% over — buy slightly extra |
| Round (tapered/flared) | Diameter for L and W | Overestimates more — round down |
| Window box / trough | Length × width × depth | Exact |
Potting Soil Needed by Container Size
If you don't want to measure, the table below gives typical soil volumes for common nursery pot sizes filled to a normal depth. These are approximate, since pot shapes vary by brand. Garden centers and references like Oregon State University Extension publish similar container-volume guides.
| Container | Approx. Volume | 2 cu ft Bags |
|---|---|---|
| 6-inch pot | 0.05 cu ft (≈1.3 qt) | — |
| 10-inch pot | 0.25 cu ft (≈6.4 qt) | — |
| 14-inch pot | 0.7 cu ft (≈18 qt) | 1 bag fills ~3 |
| Standard window box (24×8×8) | 0.9 cu ft | 1 bag |
| Half wine barrel (26 in dia) | 3.8 cu ft | 2 bags |
| 4×4 ft raised bed (12 in deep) | 16 cu ft | 8 bags |
Volumes are approximate and depend on the exact pot shape and fill depth.
Potting Mix vs Garden Soil vs Topsoil
These products are not interchangeable. Potting mix is a lightweight, soilless blend designed for drainage and aeration in containers. Garden soil is heavier and meant to be mixed into in-ground beds. Topsoil is bulk fill for leveling and large beds. Using dense garden soil in pots compacts and suffocates roots, while using airy potting mix to fill a large bed is expensive and dries out fast.
- Potting mix:
containers and hanging baskets — drains fast, holds air
- Raised-bed mix:
a blend tuned for deeper raised beds
- Garden soil:
amend in-ground beds, not pots
- Topsoil:
bulk leveling and large-volume fill
- Compost:
a nutrient amendment, not a stand-alone mix
What's in Potting Soil?
Most quality potting mixes combine a few core ingredients to balance water retention, drainage, and nutrients. Understanding them helps you choose or blend a mix and explains why potting soil is so light compared to native ground soil.
| Ingredient | Role | Typical Share |
|---|---|---|
| Peat moss / coir | Holds moisture, light structure | 40–60% |
| Perlite / pumice | Improves drainage and aeration | 10–30% |
| Vermiculite | Holds water and nutrients | 5–15% |
| Compost / bark | Adds nutrients and body | 10–30% |
| Lime | Balances pH of peat | small amount |
Worked Example: 4×4 ft Raised Bed
Suppose you're filling a 48 × 24 inch raised bed to a depth of 12 inches and want a cost estimate using $9.50 bags of 2 cu ft mix. The volume is 48 × 24 × 12 = 13,824 in³, which is 13,824 ÷ 1,728 = 8 cubic feet (about 0.30 cubic yards or 206 dry quarts). At 2 cubic feet per bag you need 4 bags, costing 4 × $9.50 = $38.00. Buying a 5th bag gives a little reserve for settling — soil compacts a few percent after watering.
Mixes settle after the first few waterings, so it's smart to buy slightly more than the exact figure.
Tips to Buy and Use Potting Soil Wisely
A few habits save money and produce healthier plants. Buying in the right format and refreshing — rather than fully replacing — mix each season are the biggest wins for container gardeners.
Compare price per cubic foot, not per bag — sizes vary
Bulk (cubic yard) delivery is cheaper for large raised-bed projects
Refresh old mix with 25–50% fresh compost instead of replacing it all
Buy ~10% extra to allow for settling and topping off
Store opened bags sealed and dry to prevent fungus gnats
One cubic yard equals 27 cubic feet — about 13–14 standard 2 cu ft bags. For big jobs, bulk is usually the better value.
Potting Soil Glossary
Key terms used when buying and using potting soil. Knowing them helps you compare products and read bag labels.
| Term | Definition |
|---|---|
| Cubic foot (cu ft) | A volume 12×12×12 inches; the standard bag unit. |
| Dry quart | A US dry volume unit; 1 cu ft ≈ 25.7 dry quarts. |
| Cubic yard | 27 cubic feet; the unit for bulk soil delivery. |
| Potting mix | A lightweight soilless blend for containers. |
| Perlite | Volcanic glass beads that improve drainage and aeration. |
| Coir | Coconut-husk fiber used as a peat alternative. |
| Water retention | A mix's ability to hold moisture for roots. |
Quick Reference Card
Potting Soil — Quick Reference
Quick reference • Potting Soil Calculator
Cubic feet = Length × Width × Depth × Quantity ÷ 1,728 (inches)Valid range: Length & width 0.1–2000 in; depth 0.1–100 in; bag size 0.1–50 cu ft
Common Values
⚠ Watch Out
- •Measure in inches; the formula divides by 1,728 for cubic feet
- •Round pots hold ~21% less than the rectangle estimate
- •Don't use heavy garden soil in containers
- •Mix settles after watering — buy a little extra
Pro Tips
- →Compare price per cubic foot, not per bag
- →Use bulk (cubic yard) delivery for large raised beds
- →Refresh old mix with compost instead of replacing it all
- →Fill to 1–2 inches below the rim to prevent overflow
FAQs
How much potting soil do I need?
Multiply the container's length, width, and soil depth in inches, then divide by 1,728 to get cubic feet. For example, a 48 × 24 inch raised bed filled 12 inches deep needs 13,824 ÷ 1,728 = 8 cubic feet, or four 2 cu ft bags. Enter your measurements above for an instant answer.
How many cubic feet are in a bag of potting soil?
Bags are most often 1, 1.5, or 2 cubic feet, though some are sold in dry quarts (a 2 cu ft bag is about 51 dry quarts). Check the label and enter your bag size so the calculator divides correctly and tells you how many bags to buy.
How many quarts are in a cubic foot of soil?
One cubic foot equals about 25.7 US dry quarts. So a 2 cubic foot bag holds roughly 51 dry quarts. The calculator shows both cubic feet and quarts so you can match whichever unit is printed on the bag.
How do I calculate soil for a round pot?
For a quick estimate, enter the pot's diameter for both length and width — you'll buy slightly extra. For precision, use the cylinder volume π × radius² × depth. Tapered pots hold less, so round down a little for flared shapes.
What's the difference between potting mix and garden soil?
Potting mix is a lightweight, soilless blend designed to drain and aerate in containers. Garden soil is heavier and meant to amend in-ground beds. Don't use dense garden soil in pots — it compacts and suffocates roots.
How deep should potting soil be in a container?
Fill to about 1–2 inches below the rim so water doesn't overflow. Most vegetables and flowers need at least 8–12 inches of soil depth for healthy roots; deep-rooted crops like tomatoes prefer 12 inches or more.
Is it cheaper to buy potting soil in bulk?
For large raised-bed projects, bulk soil delivered by the cubic yard is usually cheaper than bagged mix. One cubic yard equals 27 cubic feet — about 13–14 standard 2 cu ft bags. For a few pots, bags are more practical.
Can I reuse old potting soil?
Yes. Refresh used mix by blending in 25–50% fresh compost or new potting mix to restore structure and nutrients, rather than replacing it entirely. Discard soil from plants that had soil-borne disease.
How much does potting soil cost?
Bagged potting mix typically runs $5–$15 per 2 cubic foot bag in 2026, depending on quality and brand. Enter the price per bag in the calculator to estimate your total cost for the project.
Why divide by 1,728?
There are 1,728 cubic inches in a cubic foot (12 × 12 × 12). Since you measure containers in inches but buy soil in cubic feet, dividing the cubic-inch volume by 1,728 converts to the units printed on the bag.
Is the Potting Soil Calculator free to use?
Yes, the calculator is completely free with no registration required. You can use it unlimited times to plan containers, raised beds, and window boxes, and estimate how many bags to buy.