Your 1RM is your "One Rep Max", which is theoretically the  maximum load you can lift on any given exercise, for one single repetition.

Because there are so many factors that influence your training performance, such as your sleep from the night before, nutrition, hydration, recovery from the last session, your training environment, etc... This calculation is about as accurate as you can get, playing the numbers game and estimating based on your prior performance.

If you want an in depth article on the science behind this formula, where it came from, and how accurate it truly is, check out our 1RM Research Article.

The results from this calculation can provide you with numbers to aim for in the future, as well as give you suggested targets to hit in your weekly training sessions. For example, you may be following a program that calls for 7 reps at roughly 75% of your 1RM or 5 reps at roughly 85% of your RM, in which you would only be able to follow properly by utilizing this information. You may also use it as a way to build strength, without causing yourself too much fatigue -- i.e. train for 1-3 reps at 90%, instead of every going to 100% (same strength gains, easier to recover from).

Yes and No. Not nearly as useful as if you were after strength specifically. However, you can still use this to keep some strength specific focused lifts in your routine OR to keep yourself in a specific range and percentage of your 1RM. This is often used instead of RIR or RPE, which you can read more about in our article on the topic, but it's even more useful along side an RPE or RIR scale.