How it works
Two inches (5 cm) suits most tanks. Rooted plants do better with two to three inches. Fish-only tanks can use less.
The calculator works out the volume of the layer, then converts it to weight using a typical density: about 1.6 kg per litre for sand, 1.5 for gravel and 1.0 for plant soil. Real products vary, so treat the weight as a guide.