How to use

Pick the pot shape: tapered round pot, rectangular planter, or grow bag/polybag.
Enter the inside measurements in cm and the depth of the mix (how high the soil sits, not the rim).
Enter how many pots of this size you have.
Choose your potting mix. If you know your own mix, choose Custom and enter its wet weight per litre.
Adjust the empty pot weight, plant weight and saucer water if needed.
Enter the floor area the pots stand on to see the load in kg per m².

Have pots of different sizes? Run the calculator once per size and add the totals.

How it's calculated

Soil volume per pot (litres = cm³ ÷ 1000):

Round tapered pot (a frustum): V = π × h ÷ 12 × (D² + D×d + d²), where D is the top diameter, d the bottom diameter and h the depth of mix.
Rectangular planter: V = length × width × depth.
Grow bag: V = π × (diameter ÷ 2)² × depth.

Then:

Mix weight = volume × wet density of the mix (kg/L)
Weight per pot = mix weight + empty pot + plant + saucer water (1 L of water = 1 kg)
Total = weight per pot × number of pots
Load = total ÷ (area length × area width)

We use the weight after a thorough watering and draining, because that is the heaviest normal state — and in Malaysia a rainstorm can soak every pot at once. The densities in the list are typical approximations: bagged potting mix about 1.0 kg/L, soil + compost about 1.3, garden soil about 1.6, soil + sand about 1.8, coco peat mixes 0.6–0.7. Real mixes vary, so weigh 1 litre of your own wet mix if you want a better number.

Worked example

Six round pots, 30 cm across the top and 22 cm at the base, filled 25 cm deep with bagged potting mix:

V = π × 25 ÷ 12 × (30² + 30×22 + 22²) = π × 25 ÷ 12 × 2,044 ≈ 13.4 L of mix → 13.4 kg
Per pot: 13.4 + 1 kg pot + 1.5 kg plant + 0.5 kg saucer water ≈ 16.4 kg
Six pots ≈ 98 kg
Standing on a 2 m × 1 m strip of balcony: 98 ÷ 2 ≈ 49 kg/m²

Switch the mix to garden soil (1.6 kg/L) and the same six pots come to about 146 kg — a big difference for the same pots.

Important: this is an estimate, not a safety approval

Only the building's structure decides how much weight a balcony, ledge or rooftop can carry. Check the allowed load with your building management (JMB/MC) or a qualified engineer before putting heavy planters, raised beds or water tanks on it. The calculator helps you give them a realistic number.

Tips to keep weight down

Use a lighter mix: coco peat with compost and perlite weighs far less than garden soil when wet.
Use plastic pots or grow bags instead of clay or ceramic.
Don't use deeper pots than the crop needs — leafy greens are happy in 15–20 cm of mix.
Empty saucers after rain so water does not sit there.
Place the heaviest pots close to the building wall, not at the outer edge of the balcony.

CalculatorsSowing Density & Seed CalculatorSowing density calculator: how many plants fit your bed or pot and how many seeds to sow for kangkung, choy sum, lettuce, chili, tomato and more.

GuidesBalcony Vegetable Garden in Malaysia - A Beginner's GuideGrow vegetables on a condo or apartment balcony in Malaysia - sun by direction, wind, weight, containers, easy first crops, watering and building rules.

FAQ

Why use wet weight instead of the weight of the bag? Mix soaks up water. A pot right after watering or rain is much heavier than when it was dry, and that is the weight the floor must carry.

Does the calculator include people or furniture? No. It only counts pots, mix, plants and saucer water. Your engineer will consider everything else on the balcony.

How do I find my mix's density? Fill a 1 litre container with mix that has been watered and drained, then weigh it. Enter that figure as Custom.

Is a grow bag lighter than a pot? The bag itself is lighter, but the mix inside weighs the same for the same volume. Most of the weight is always the wet mix.