About

Balcony gardening requires strict adherence to structural load limits. Wet soil is significantly heavier than dry potting mix, often exceeding 50% more mass after irrigation. This calculator determines the exact volume of substrate required for rectangular boxes, cylindrical pots, or trough planters and estimates the total weight at full water saturation. Calculating volume ensures sufficient root space for plants while preventing the purchase of excess soil sacks, reducing waste and physical strain during transport.

Formulas

Volume calculations depend on the container geometry. Weight is derived from the product of volume and the density of the chosen saturated medium.

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Rectangular: V = L × W × DCylindrical: V = π ⋅ d²4 ⋅ hWeight: W_total = V × P_wet

Where P_wet represents the density of the water-saturated substrate.

Reference Data

Material	Dry Density (kg/L)	Wet Density (kg/L)	Use Case
Standard Potting Mix	0.35 - 0.45	0.80 - 0.95	General flowers/herbs
Topsoil (Loam)	1.10 - 1.25	1.60 - 1.90	Raised beds (Heavy!)
Coco Coir	0.07 - 0.10	0.60 - 0.80	Lightweight mix
Compost	0.50 - 0.60	0.90 - 1.10	Nutrient additive
Perlite/Vermiculite	0.10 - 0.15	0.30 - 0.40	Aeration (Very light)
Sand	1.45 - 1.60	1.90 - 2.10	Drainage/Succulents

Frequently Asked Questions

Soil is porous. When you water a plant, water fills the air gaps between particles. Water weighs 1 kg per liter. A light, fluffy potting mix can double or triple in weight when fully saturated.

No. The calculation covers only the soil and the water it holds. Ceramic, terracotta, or concrete pots add significant static load (often 5-15kg empty) which must be added to the total calculation for balcony safety.

Typically 10-20% of the pot's height. This calculator determines the *total* internal volume. If using gravel for drainage, subtract that volume from the soil purchase requirement, but account for the gravel's high density (approx 1.6 kg/L).

While codes vary by region and building age, modern residential balconies are often rated for 200-400 kg/m². Always check your specific building blueprints or lease agreement, especially for older structures.