A potting run is a number of pots, each holding a known volume of mix. Bagged media is sold by the cubic foot; pots are sized in quarts or gallons. A cubic foot is 25.71 dry quarts, so pots times quarts per pot over bag cubic feet times 25.71 is bags, and ROUNDUP makes sure the crew does not run out of soil three flats from the end.
400 one-gallon pots at 1.5 qt of mix each is 600 quarts. A 2 cu ft bag holds 51.42 qt, so 11.67 bags — pull 12.
The example
Three runs with three bag sizes. Quarts per pot is the fill volume, not the nominal pot size — a "one-gallon" trade pot holds about 3 quarts and is filled to about 2.5.
| A | B | C | D | E | F | |
|---|---|---|---|---|---|---|
| 1 | Run | Pots | Qt per pot | Bag (cu ft) | Quarts | Bags |
| 2 | 1-gal perennials | 400 | 1.5 | 2 | 600.0 | 12 |
| 3 | 4-inch annuals | 1,200 | 0.75 | 2 | 900.0 | 18 |
| 4 | 3-gal shrubs | 150 | 4 | 1.5 | 600.0 | 16 |
The formula
Quarts first, so it can be checked against the last run, then bags:
How it works
The 25.71 is the whole trick; the rest is arithmetic:
B2*C2is total quarts of mix. Measure the fill on a few pots with a quart scoop rather than trusting the pot label.D2*25.71is quarts in one bag. A cubic foot is 25.71 dry quarts, so a 2 cu ft bag is 51.42 qt and a 1.5 cu ft bag is 38.57.E2/(D2*25.71)is bags as a decimal. 600 over 51.42 is 11.67.ROUNDUP(...,0)makes it 12. Media settles and spills; the partial bag is not optional.
Bulk media by the cubic yard uses the same formula with 27 cubic feet per yard: =ROUNDUP(E2/(27*25.71),1) gives yards to a tenth, which is how the supplier will quote it.
Try it: interactive demo
Enter the pot count, the fill per pot in quarts, and the bag size in cubic feet.
Variations
Liters and litre bags
Metric media is sold in liters and pots are filled in liters, so no conversion: pots times liters per pot over bag liters.
Media cost per pot
Bags times bag price, divided by pots, is the soil cost that goes into the plant's cost sheet.
Pitfalls & errors
Compressed bales are not bags. A 3.8 cu ft compressed peat bale fluffs to 7 or more cubic feet. Use the expanded volume, or the sheet will order twice the peat you need.
Track actual bags used against the formula for a few runs. If the crew consistently uses 10 percent more, put a waste factor in the formula rather than arguing with them.
Do not mix liquid quarts and dry quarts. A liquid quart is 0.946 L and a dry quart is 1.101 L. Potting mix is measured dry, and the 25.71 constant assumes it.
Practice workbook
Frequently asked questions
Where does 25.71 come from?
How do I get quarts per pot?
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