Urban planter boxes come in many sizes, so the weight of a filled box is a range rather than a single figure. As a practical guide, a typical medium urban planter box—about 90 × 40 × 40 cm (roughly 35 × 16 × 16 in)—will usually weigh around 75–180 kg (165–400 lb) when filled with moist soil. The container itself might weigh 8–30 kg for plastic or wood, while the soil and water make up most of the total. Smaller balcony boxes around 60 × 25 × 25 cm often weigh 25–60 kg (55–130 lb). Large rooftop or commercial planters can reach 250–500 kg (550–1,100 lb) or more.
To estimate the weight, calculate the soil volume: length × width × soil depth in metres gives cubic metres; multiply by 1,000 to get litres. Then multiply the litres by the soil density. Moist potting mix is roughly 0.6–1.0 kg per litre, ordinary topsoil is about 1.2–1.6 kg per litre, and saturated soil can be even heavier. Finally, add the weight of the planter and allow for water.
For example, a box measuring 90 × 40 × 35 cm holds about 126 litres. With moist potting mix at 0.8 kg per litre, the soil weighs about 101 kg; adding a 15 kg planter gives a total of roughly 116 kg. If the same box were filled with dense topsoil at 1.4 kg per litre, the soil alone would weigh about 176 kg, and the total would be around 191 kg with the planter.
In practice, most urban planter boxes are not filled right to the rim. Leaving 2–5 cm of space for drainage, watering, and mulch reduces the soil volume slightly. Wet soil is also significantly heavier than dry soil, so the weight can rise after rain or watering. For balconies, roof terraces, and indoor spaces, always check the load limit, use a lightweight potting mix where possible, and consider casters or a trolley for large containers. In short, a typical medium urban planter box filled with soil usually weighs somewhere between 75 and 180 kg, but smaller and larger designs can fall well outside that range.