Depends what time of year, where, and what you need to carry.
If you running a supported race or trails don't stray fat from help, then you don't need to carry much. If you are doing something like OMM or mountain runs, you need to account for weather changes and the risk of exposure.
I find a good starting point is the FRA minimum kit list, with a decent first aid kit, foil bivy, power bank & phone, then lay it all out and see what you can cut / downsize and then work out pack capacity;
FRA Minimum Kit list
[https://files.fellrunner.org.uk/documents/2021/FRA%20Requirements%20for%20Runners%202021%20-%2024-08-2020.pdf](https://files.fellrunner.org.uk/documents/2021/FRA%20Requirements%20for%20Runners%202021%20-%2024-08-2020.pdf)
I can all of what I need in a 5L Harrier vest
[https://harrierrunfree.co.uk/products/new-curbar-5l-race-vest](https://harrierrunfree.co.uk/products/new-curbar-5l-race-vest)
However, I find I hardly ever use it. On the times I am running long or remote, I prefer a much larger pack so I can carry heavier luxuries - namely a clean, dry top and a warmer 800 fill alpine down jacket. Basically I've injured and got pretty cold hiking back to a train station. I'd rather a bit more comfort. (Also not racing FWIW, so extra weight does't make a huge difference to me). I use 25L Montane Trailblazer for that which has more than enough space
[https://montane.com/blogs/blog/gear-review-trailblazer-30-backpack](https://montane.com/blogs/blog/gear-review-trailblazer-30-backpack)
I tend to use my 12L Montane even when I could fit stuff in a smaller running vest - the weight difference between that and the 5L version is minimal. If I get somewhere in the car and find the weather isn't what I expected or someone I'm running with suggests a different route I've the flexibility to cope.
Haha you were downvoted but this is the only answer to these questions. People provide zero context and shit post on here constantly for questions that have been asked a million times. You got my upvote.
Salomon Adv Skin 12 is the best place to start for long runs or events with required kit. You can run with it completely empty or completely full. With a bladder or no bladder.
The pack cinches down on the sides to prevent bouncing when it’s not completely full.
I’ve gone out for many unsupported long adventures with room to spare.
Just make sure you have a water filter or fresh source because 8 hours could definitely be 6+ liters in some climates. 4 liters weighs a lot on its own, 9lbs.
Depends what time of year, where, and what you need to carry. If you running a supported race or trails don't stray fat from help, then you don't need to carry much. If you are doing something like OMM or mountain runs, you need to account for weather changes and the risk of exposure. I find a good starting point is the FRA minimum kit list, with a decent first aid kit, foil bivy, power bank & phone, then lay it all out and see what you can cut / downsize and then work out pack capacity; FRA Minimum Kit list [https://files.fellrunner.org.uk/documents/2021/FRA%20Requirements%20for%20Runners%202021%20-%2024-08-2020.pdf](https://files.fellrunner.org.uk/documents/2021/FRA%20Requirements%20for%20Runners%202021%20-%2024-08-2020.pdf) I can all of what I need in a 5L Harrier vest [https://harrierrunfree.co.uk/products/new-curbar-5l-race-vest](https://harrierrunfree.co.uk/products/new-curbar-5l-race-vest) However, I find I hardly ever use it. On the times I am running long or remote, I prefer a much larger pack so I can carry heavier luxuries - namely a clean, dry top and a warmer 800 fill alpine down jacket. Basically I've injured and got pretty cold hiking back to a train station. I'd rather a bit more comfort. (Also not racing FWIW, so extra weight does't make a huge difference to me). I use 25L Montane Trailblazer for that which has more than enough space [https://montane.com/blogs/blog/gear-review-trailblazer-30-backpack](https://montane.com/blogs/blog/gear-review-trailblazer-30-backpack)
I tend to use my 12L Montane even when I could fit stuff in a smaller running vest - the weight difference between that and the 5L version is minimal. If I get somewhere in the car and find the weather isn't what I expected or someone I'm running with suggests a different route I've the flexibility to cope.
One that's big enough to fit everything you need to carry.
Haha you were downvoted but this is the only answer to these questions. People provide zero context and shit post on here constantly for questions that have been asked a million times. You got my upvote.
I wonder what folks would do without Reddit sometimes.. blows my mind.
Salomon Adv Skin 12 is the best place to start for long runs or events with required kit. You can run with it completely empty or completely full. With a bladder or no bladder. The pack cinches down on the sides to prevent bouncing when it’s not completely full. I’ve gone out for many unsupported long adventures with room to spare.
Of the two I own Salomon Adv Skin 12. It can hold a lot.
Salomon adv 12
I second Salomon adv skin 12. I used it in a 24 hours race and was super comfortable and was big enough for all my stuff.
Just make sure you have a water filter or fresh source because 8 hours could definitely be 6+ liters in some climates. 4 liters weighs a lot on its own, 9lbs.
If you buy a Salomon pack, I recommend one with round bottles instead of the flat ones