Guide
Container soil weight: what a pot actually weighs once you water it
Bags of potting mix are sold by volume, balconies are rated by weight, and the conversion between the two changes by a factor of three the first time you water. Here are the numbers to convert with.
The two constants everything else hangs on
Water weighs 8.34 lb per US gallon (62.4 lb per cubic foot, 1 kg per liter), and a cubic foot holds 7.48 gallons. Every weight below is just a material's dry density plus however much water it holds. Peat- and coir-based mixes are the extreme case: they're light and spongy dry, and can hold around half their volume in water at saturation, which is why a bag you carried up the stairs one-handed becomes a pot you can't slide across the floor.
Weight by material
| Material | Dry, per cu ft | Saturated, per cu ft | Saturated, per gallon |
|---|---|---|---|
| Potting mix (peat/coir based) | 10–15 lb | 40–60 lb | 5–8 lb |
| Garden topsoil (mineral) | 75–100 lb | 100–120 lb | 13–16 lb |
| Compost | 30–45 lb | 55–75 lb | 7–10 lb |
| Gravel mulch / drainage rock | 95–105 lb | 100–110 lb | 13–15 lb |
| Water, for reference | — | 62.4 lb | 8.34 lb |
The ranges are real, not hedging: dry weight depends on the recipe (more perlite is lighter, more compost or sand is heavier), and saturated weight depends on how recently you watered and how freely the container drains. For load planning, use the top of the range — a container is at its heaviest ten minutes after a thorough watering, and that's the state your floor has to carry.
Worked examples
| Container | Volume | Wet potting mix | Wet garden soil |
|---|---|---|---|
| 5-gal bucket | 0.67 cu ft | 27–40 lb | 67–80 lb |
| 10-gal pot | 1.34 cu ft | 54–80 lb | 134–160 lb |
| 20-gal pot | 2.67 cu ft | 107–160 lb | 267–320 lb |
| 15-gal tomato container | 2.0 cu ft | 80–120 lb | 200–240 lb |
So the short answer to the common question: a 20-gallon pot of wet potting mix weighs roughly 110 to 160 pounds — before the pot itself (a ceramic one can add 20–40 lb), the plant, and any gravel layer. The same pot filled with garden soil is in the 270–320 lb range, which is the practical argument for never filling balcony containers with dug soil, on top of the drainage and disease arguments.
Reading these numbers against a balcony
US balcony live-load minimums commonly run 40 to 60 pounds per square foot — the full background is in our balcony weight limits guide. A 20-gallon pot has a footprint of roughly 2 square feet, so at 160 lb wet it's applying about 80 psf where it stands. That's fine as one pot among furniture-scale loads spread across a slab, but a row of them along a railing concentrates weight exactly where the guide says not to. Spreading containers out, keeping the heavy ones near the building wall, and choosing potting mix over soil are the three levers that matter.
Weight is also a reason to size pots honestly rather than generously. Our container size chart lists the recommended volume per crop — going one size up from that is comfort; going three sizes up is a hundred pounds of wet mix the crop will never use.
One habit makes all of this concrete: weigh one watered pot once on a bathroom scale. Your mix, your watering style, one real number — and every other container on the balcony becomes a multiplication problem instead of a table lookup.