as a result of more leg speed.l know other factors affect your mile time aside from leg speed.

My current 400m is 62 sec and my mile time is 5:08
I've never done speed work and l have weak legs.Assuming l can drop my 400m to 54 sec, what mile time could l possibly run if l maintian the same conditioning.

Now this is just an answer from personal experience, so do not put much scientific basis behind this. My freshman year of high school, l could run the 400 in about 60 flat, and my time in the mile was 4:54. This seems comparable to you right now.
By junior year l ran a 54 second 400, and l could run the mile in 4:40.

l hope that helps. Speed work always helps you become a faster miler by the way. Good luck.

Your mile time compared to ur top 400m seems pretty typical to me, based on when l was in high school running similar times. l never was much for speed work either.

If u could somehow drop ur 400m time to 54 seconds, I'd say u will drop ur mile into the 4:30-4:40 range, depending on the rest of ur conditioning.

It really is not about what kind of times u can run for a single 400m, its about having consistent, repeatable 400m speed. You can run a single 400m at 62 seconds. If u could do 5 or 6 400m repeats at 62 seconds, then ur mile time would probably fall to the mid 4's. Do not focus so much on ur ''best'' 400m, focus on what kind of 400m u can do over & over again without ur times slowing down from one rep to the next. You're talking about a 54 second 400m, but what if u just conditioned to be able to maintain ur 62 second pace without worrying about making ur laps faster? Who would u be racing who could stand up against a 4:08 mile?

l run very very similar times so l think if ur get ure 400 to 54 sec (which will be loads of work) u will probably see ure 1600 around 4:50. But u have to remember to not just train for the 400 but at the same time train for the mile or else u will lose ure endorence.