Mine are (according to Axiom) 27.5L. Yesterday's load was: 1 quart pho leftovers, 1 rain jacket, bottle of prosecco, 1lb coffee can, 5lbs granola, 10lbs frozen chicken, 4 lbs frozen veggies, a bunch of flowers, my U lock, and a small shoulder strap purse. Oh, and a bungee net since I wasn't sure if I'd end up with overflow.

The jacket isn't very packable, or I could have squeezed more in.

The main downside of my panniers is I spend a fair bit of time snarling at the hook on the lower bungees. They like to have bungee sex with each other. They like to catch on grocery carts. They like to engage in exotic mating dances with my rack... I have no worries about the panniers falling off the rack tho.