Long time lurker, first time poster.
I have a Vango Ibex 50 rucksack that I bought about 15 years ago. I'm heading on a 3 day hike and it will be big enough but in comparing with a friend who has a Macpac 65 litre, it seems that mine is not much smaller

Anyone that might have one that can shed some light or let me know how I can easily measure the total volume of mine.
Cheerio,
Mark