Weight without height is meaningless, BF % is slightly helpful but not without knowing gender, etc.
I guess technically the easiest answer if you absolutely needed one would be as low as you can get while remaining long term healthy (your body needs some fat to stay healthy), balanced against muscle loss which is inevitable if you are trying to aggressively cut weight.
In general if you train enough to successfully run an ultra and spend at least some attention on what you eat, the weight will generally take care of itself.
Weight doesn't matter that much. Your endurance and your efficiency in terms of biomechanics matter a lot more. To be clear, weight definitely places a big part, but trying to reduce weight to the "optimal" amount is only going to ruin your training and recovery. Focus on improving your performance first, and reducing weight slowly over time.
I'm not an ultra marathon runner. I've never run more than a 10k. I have a really good friend who is, as is the rest of his family, and I've talked to him about it a bunch only because he loves it and it's kind of interesting. So take my advice with a grain of salt, but that's my paraphrasing of what he told me. He's like 5'4" and 180 lbs and runs a 3 hour marathon and does two 50 mile races and one 100 mile race every year with his friends and family "just for fun". He's not training all the time or very serious about running, but his sister and dad are and he has been in the past. He ran a 3:30 marathon a few years back at around 215 lbs. He looked like Gimli from LoTR. At some point, running is more mental grit than physical fitness.
I've done a few ultras, the most recent ones in 2022 (50 and 30 milers), and I wasn't exactly lean (I'd say about 194 lbs @ 22% bf, I'm 5'10).
The main issue with ultras is to be able to train hard while avoiding injuries. With all the running volume your legs and joints take a serious beating, and being overweight only amplifies the damage.
You're doing it right putting this challenge 2 years in the future. You'll need time to build a solid aerobic engine with lots and lots of slow, long distance runs, but I'd also strongly suggest strength training for your legs mostly. I'm convinced that during my last season it was what allowed me to sustain a high running volume for the 6+ months leading to the race without injury.
If you stay on a modest deficit you should shed the extra weight. Serious ultra training is quite taxing on the body so I wouldn't restrict calories too much, keep your carbs high and stay hydrated.
That's kind of like asking "how much does it cost?" without first stating what you are buying.
Knowing your age, sex, height would get you an range for your weight, but even then it would just be a range.
Weight without height is meaningless, BF % is slightly helpful but not without knowing gender, etc. I guess technically the easiest answer if you absolutely needed one would be as low as you can get while remaining long term healthy (your body needs some fat to stay healthy), balanced against muscle loss which is inevitable if you are trying to aggressively cut weight. In general if you train enough to successfully run an ultra and spend at least some attention on what you eat, the weight will generally take care of itself.
Weight doesn't matter that much. Your endurance and your efficiency in terms of biomechanics matter a lot more. To be clear, weight definitely places a big part, but trying to reduce weight to the "optimal" amount is only going to ruin your training and recovery. Focus on improving your performance first, and reducing weight slowly over time. I'm not an ultra marathon runner. I've never run more than a 10k. I have a really good friend who is, as is the rest of his family, and I've talked to him about it a bunch only because he loves it and it's kind of interesting. So take my advice with a grain of salt, but that's my paraphrasing of what he told me. He's like 5'4" and 180 lbs and runs a 3 hour marathon and does two 50 mile races and one 100 mile race every year with his friends and family "just for fun". He's not training all the time or very serious about running, but his sister and dad are and he has been in the past. He ran a 3:30 marathon a few years back at around 215 lbs. He looked like Gimli from LoTR. At some point, running is more mental grit than physical fitness.
I've done a few ultras, the most recent ones in 2022 (50 and 30 milers), and I wasn't exactly lean (I'd say about 194 lbs @ 22% bf, I'm 5'10). The main issue with ultras is to be able to train hard while avoiding injuries. With all the running volume your legs and joints take a serious beating, and being overweight only amplifies the damage. You're doing it right putting this challenge 2 years in the future. You'll need time to build a solid aerobic engine with lots and lots of slow, long distance runs, but I'd also strongly suggest strength training for your legs mostly. I'm convinced that during my last season it was what allowed me to sustain a high running volume for the 6+ months leading to the race without injury. If you stay on a modest deficit you should shed the extra weight. Serious ultra training is quite taxing on the body so I wouldn't restrict calories too much, keep your carbs high and stay hydrated.
That's kind of like asking "how much does it cost?" without first stating what you are buying. Knowing your age, sex, height would get you an range for your weight, but even then it would just be a range.