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A 60 litre bag of dry compost generally 15.2 Kg. There are a few reasons why the compost in a bag may weigh more than 15.2 Kg. Moisture content and soil content are all factors that need to be taken into consideration when assessing the weight of a bag of compost. In this article, we look at all the contributing factors that affect how much a bag of compost might weigh.

For the sake of simplicity, we are using the word “weight” loosely, because that’s what the layman understands as how heavy an object is. Strictly, it should be mass but let’s not make it too complicated.

To know how much a bag of compost weighs, we need to understand the difference between volume (how much space an object takes up) and weight (how heavy an object is).

How Many Feathers are in a Ton?

Do you remember the school day joke, “What weighs more a tonne of feathers or a tonne of bricks?”. Of course, they both weigh the same but the difference in volume is miles apart! There is an average of 330 bricks in a tonne which would use approximately 1 cubic metre of space but it would take approximately 110,600,000 feathers to make a tonne, approximately 400 cubic metres of space!

How Much does Compost Weigh?

Although compost from the garden centre is usually stored in plastic sacks, it can still soak up moisture and this will make the bag feel heavier, so don’t expect every bag of compost to weigh the same. Compost often has added John Innes to help with moisture retention and permanent plantings in pots. We have weighed some garden centre bags to give a rough guide on how much compost weighs;

  • 60 Litre bag of Multi-Purpose Compost weighs 15.2 Kg.
  • 30 Litre bag of John Innes No3 weighs 18 Kg.
  • 50 Litre bag of wet Tree and Shrub Compost weighs 22 Kg.
  • 1 cubic metre bag of manure weighs approximately 380 Kg.

Why is Compost Measured in Litres –

Volume and Weight (mass)

This is important because it explains why compost is measured in Litres (volume) and not Kilograms (weight). Compost can be made up of many different ingredients, e.g. Bark, vegetable matter and soil and how much moisture each of those ingredients hold. This means every bag of compost could have a slightly different weight. However, it is possible to say how much space the compost uses (volume). This unit is measured in litres or cubic metres

To simplify this, imagine a box 10 cm high x 10cm long x 10cm wide, that box would hold 1 litre of compost. Now imagine 1000 of those boxes stacked in a cube, this would make up one cubic metre.

In the world of gardening, you could assume there are 10 x 100 litre bags of compost in a 1 cubic metre bag also known as a tonne bag or builders bag!

cubic metre ton bag of compost vs garden centre bags of compost
Tonne bag of compost Vs Garden centre bags of compost