Compost sold in litre bags

[Dom Tuk]

Why is compost (a solid material) sold in litres and not kilograms? Are there any other solid products that are sold as litres which is traditionally a liquid measurement.

[brachiopod]

Compost is sold by volume, as the weight can vary (volume for volume) with the water content.

The retail industry requires a standard product that is easily and uniformly packed and priced. To start making adjustments for variances due to excess water would be extremely complicated. ("These bags are 50p off mate, 'cos they were packed when it was raining" or "There's an extra two kilo's in this bag, 'cos it's wetter than the last batch.")

As a comparison, an arable farmer selling his truckload of wheat to a wholesaler will sell it by weight at the agreed price per tonne. However, a number of samples are taken and the water content of that batch is assayed. The gross weight is then adjusted to give a net weight for which he is paid.

The qualitative sampling required in the latter example is impractical when you just want to grab a bag of compost from B&Q.