One Rep Max
A classic measure of strength is the maximum weight you can lift for one repetition.

This calculator estimates your one rep max.  Use this tool on a regular basis to see how your strength is increasing through regular weight training.
Instructions
Perform one set of a given excercise to positive failure (up to 12 repetitions).

Input the weight lifted and repetitions performed. 

Press the Calculate button.

Note: This calculator works in either kilograms or pounds.

This calculation should not be taken as an absolute.  Remember, if you have been doing high rep sets for the past several months, you are not going to be able to handle the one rep max that this calculator says you should.  This is due to a lack of tendon strength and raw power necessary to lift low rep weights.

In order to improve your one rep max, you must train close to that rep range.  In other words, practise.

Warnings:

Please do not perform this exercise unsupervised.  You will be lifting what is a very heavy weight for you.  One or more strong people should be with you in case you cannot complete the lift.

Pain is a warning signal to stop before you hurt yourself.

A strong grip and precise concentration will help you to complete this exercise safely.

Stretching is very important, especially when you are lifting a heavy weight and putting strain on your muscles and tendons.  When lifting a heavy weight, stretching will help you to prevent aching joints and other nuisances that can put an end to your heavy lifting days.
 
Weight Lifted Reps Performed One Rep Max