We get asked for rotor spec books on a weekly basis. Used to be, brake manufacturers would publish a new book every other year or so and hand them out free of charge. Used to be, rotors were a major purchase. These days rotors are fairly inexpensive and manufacturers don't hand out much of anything without a price tag.
The quickest way to get specs for your car or truck is to use an online catalog like the Raybestos brake catalog. Click in the year, make and model and then select front or rear rotor. A final click on the part number will bring up a new window with a variety of specs including the minimum thickness. You'll need a decent micrometer to measure your existing rotor to decide whether they can be saved by machining. With most new rotors being lighter and therefore thinner there is not much leeway. Thickness is just one aspect. If they are close to the limit and have a vibration or wobble you will surely need new steel. Machining material from a rotor that is warped will lead to further warping as there is less mass to fight off the forces that heat applies to the rotor.