Chin up 1rm vs pull up 1rm

How much more weight can you normally chin compared to a prone grip pull up? I want to compare my current chin up strength to my pull up strength of my youth, to gauge my progress. I never did chin ups before but I did a double bodyweight pull up at about 180 pounds, and could also do a few unilateral chins. I am guessing it's normal to chin about 10-15% more weight than you can pull up, because of the involvement of the biceps. I also curled 150 pounds so my biceps strength was decent. Anyway I'm estimating my best chin up would have been somewhere around 400 pounds combined total weight. So when I progress in my training to 350 for 3 sets of 5, I'll know I've surpassed my previous strength.

I've become somewhat obsessed with keeping track of my "starting strength total" (all 6 exercises) relative to the best lifts of my prime, so I can know for sure at what point in my training I've become generally stronger than I once was.

I'd really love to see a video of a 400-pound chinup.

Haha - guess I better knock my goals down a bit. I still can't imagine my chin up could be less than my pull up. But maybe it would have been with full ROM. My pull ups and unilaterals were always just barely chin over the bar. I actually did just find a video of a 250 pound guy chinning an extra 150, but his chin barely went over the bar. So, it doesn't count.

There is no standard for the chin up. So I have to try to figure it out. For the sports I do it's probably one of the most important metrics. Maybe I'll just test a max weighted pull up and chin up and see if there's any difference.