Short answer: there is no single weight, but a typical mid-sized urban planter box—about 18–24 inches (45–60 cm) wide and made of plastic, resin, or composite—usually weighs 15–50 lb (7–23 kg) empty. Small plastic window boxes can be as light as 2–6 lb (1–3 kg). Large fiberglass, wood, metal, or concrete planters can range from 40 lb (18 kg) to 500 lb (227 kg) or more empty, depending on material and wall thickness.
Material is the biggest factor. Plastic and resin planters are the lightest and easiest to move. Fiberglass and composite are sturdier and often land in the 20–110 lb (9–50 kg) range for medium to large sizes. Wood boxes are moderate, commonly 20–80 lb (9–36 kg) for a 2–4 ft length. Metal planters vary widely: aluminum is light, while steel can be surprisingly heavy. Concrete, stone, and ceramic are the heaviest; a typical concrete streetscape planter can easily weigh 100–500 lb (45–227 kg) or more before soil.
Size matters just as much. A planter’s empty weight rises with volume, wall thickness, double-wall construction, drainage reservoirs, liners, brackets, and casters. Self-watering models add extra plastic and a water reservoir, so they can weigh more than a simple pot of the same volume.
If you are choosing a planter for a balcony, rooftop, or roof garden, check the product specifications rather than guessing. The empty weight is only part of the load. Saturated potting soil weighs roughly 80–100 lb per cubic foot (1,280–1,600 kg/m³). A 2 ft × 2 ft × 1.5 ft planter can hold about 6 cubic feet of soil, which may add 480–600 lb (218–272 kg) once wet. Add the plants, water, and the planter itself, and the total load can become very high.
For most residential urban gardens, a mid-sized plastic or composite planter at 15–50 lb (7–23 kg) empty is a practical benchmark. For commercial streetscapes or permanent installations, concrete and fiberglass planters are common, but their empty weights often start at 100 lb (45 kg) and can exceed 500 lb (227 kg). Always confirm the exact model’s weight and the load capacity of your balcony, roof, or terrace before filling it.