You can time your sprints yourself using a video camera at the finish in front of you... you can then multiply the number of frames in your sprint with the associated time per frame and get your result.
Well... the most I ever used was 40 kg dumbbells but could only do 5 reps because my hand would just unfold and drop the dumbbell... I even used 45 kg ones for 3 reps.
It's never been a leg strength issue for me with dumbbells. But I kinda like to use them because I also challenge my grip strength so...
No but seriously... think about it - if 12 (11) year old girls are at your level at similar bodyweights... where does that put you? It's not about me "shaming" you or whatever... the point is that you must acknowledge the fact that you're very weak and that is the only thing you should worry about.
No need in overanalyzing being weak. Just go out there and work and shut up. That includes myself.