This calculator will let you know how much potting soil you’ll need for a standard flower pot. The calculator will even give you options based on different common bag sizes of potting soil Just select the planter’s shape, enter its dimensions and the calculator will do the rest.
This calculator was designed specifically for regular tapered plant pots and cylinder-shaped plant pots.
If you have a square or rectangular planter, use the Topsoil Cubic Feet Yards And Bags Calculator
If you want to make the calculations yourself, here are the two formulas used for each pot type. Otherwise, just skip to the bottom to use the calculator.
Common Flower Pot Sizes And Capacity
Here are capacities for common tapered flower pot sizes
| Top Diameter | Bottom Diameter | Height | Cubic Inches | |
|---|---|---|---|---|
| 4″ Pots | 4 1/2″ | 2 4/5″ | 3-3/4″ | 40 |
| 6″ Pots | 6 5/8″ | 4 1/2″ | 5 1/8″ | 126 |
| 8″ Pots | 8 7/8″ | 6″ | 6″ | 195 |
| 10″ Pots | 11 1/8″ | 7 1/2″ | 7 3/4″ | 534 |
| 12″ Pots | 13 1/4″ | 8 7/8″ | 9 1/2″ | 925 |
| 14″ Pots | 15 5/8″ | 10 1/2″ | 11 3/8″ | 1815 |
How To Calculate Potting Soil For A Tapered Flower Pot
Most flower pots are tapered. A tapered flower pot is one that is wider at the top and narrower at the bottom. The formula you would use would be the same as the formula used to calculate the volume of a truncated cone.
It’s a crazy formula, but to start you will need to know the width of the bottom and top of the flower pot as well as its height.
Example formula for an 8 inch tall pot with a top opening of 14 inches and base of 9 inches.
Divide the top diameter in half (14 / 2 = 7) to find the top radius. Divide the bottom diameter in half (9 / 2 = 4.5) to find the bottom radius.
Then enter your height, bottom radius and top radius into the following formula:
π * height * ((bottom radius *bottom radius) + bottom radius * top radius + (top radius*top radius)) / 3
Just for reference, pi (π) equals 3.141592653.
After you’ve entered the dimensions of the pot in our example, the formula should look like this:
3.141592653 * 8 * ((4.5 * 4.5) + 4.5 * 7 + (7 * 7)) / 3
Using this formula, our 14 x 9 x 8 inch pot equals 844.0412261060001 cubic inches
If we needed to know how many cubic feet, we would divide cubic inches by 1728.
How To Calculate Potting Soil For Cylinder-Shaped Flower Pot
Cylinder shaped planters have the same diameter at the base and at the top. To find their volume, we just need to know their height and width.
Let’s say our planter is 8 inches in diameter and 12 inches in height.
- Divide the pot’s diameter (8″) in half to find it’s radius (8 / 2 = 4)
- Square the radius (4 * 4 = 16)
- Multiply the height (12″) by the squared radius (16 * 12 = 192)
- Multiply that by pi 3.1416 (192 * 3.1416 = 603.1872 cubic inches)
If we needed to know how many cubic feet, we would divide cubic inches by 1728.
Common Nursery Container Sizes
| Pot Height | Pot Width | Nursery Size | Cubic Feet |
|---|---|---|---|
| 4 1/2″ | 4 3/4″ | 1.5 quart | .05 |
| 6 1/2″ | 6 1/2″ | 2.5 quart | .12 |
| 7 3/4″ | 7″ | #1 – 1 gallon | .17 |
| 9 1/2″ | 9 1/2″ | #2 – 2 gallon | .39 |
| 10″ | 11″ | #3 – 3 gallon | .55 |
| 11″ | 12″ | #5 – 5 gallon | .72 |
| 11 1/2″ | 14″ | #7 – 7 gallon | 1.02 |
| 15″ | 15 3/4″ | #10 – 10 gallon | 1.69 |
| 16″ | 17 3/4″ | #15 – 15 gallon | 2.29 |
| 18″ | 23 3/4″ | #25 – 25 gallon | 4.61 |
If you’re mixing your own potting soil, you might also like DIY Soilless Potting Mix Recipe Calculator and DIY Soil-Based Potting Mix Recipe Calculator
