Hi Ands are you possibly confusing size of bag with volume?

Apart from dimensions there are a number of other factors you would have to consider e.g. the specific gravity of the contents, and how much they have been compacted.

Compost bags are generally less compacted than growbags so I guess it would be virtually impossible for the user to work out true capacity.

Just as a matter of interest why did you want to know?

The dimensions you give do work out at 15.8 litres. Are those sizes printed on the bag or did you measure them yourself? Would the compacted compost double in size once its watered thoroughly?

For the dimensions given the volume is 0.015675 cubic metres ,this equates to 15.6 ltrs, as 1m3 (one cubic metre)equates to 1000ltrs.We must assume that in an unpacked state the compost is around double the volume of that when packed, the makers will no doubt point out the savings in plastic packaging .

Thanks for your comments. The grow bags must somehow be compacted to double their original volume. Sorry Moon-Growe but you can calclulate volume from size, as the others have shown. The real reason I wanted to know was that Morrisons had some J Aurthur bowers grow bags on offer for 2 for £2.50 but when I calculated the voume I was disapointed. I worked out about 16 litres too. It was only when I searched the internet I realised the other maufacturers quote the same kind of 'compaction' ratio.
Many thanks all - I bought 8 of them anyway.

I know you can calculate volume from size but not if, as is usual with compost and the like, it is compressed into the bag. 66 litres for £2.50 is a reasonable price - assuming the compost is a good quality. Bulba and I tend to buy the larger bales from B & Q or our local GC.

Oh dear, now I've read the whole of this thread, twice, but no, my brain refuses to grapple with the calculations - you might as well be speaking Swahili to me. Sad ain't it...

lol