The best way to tell when any steak is cooked is to use a meat thermometer. Each level of doneness corresponds to a certain internal temperature. Check out my handy meat temperature chart to help with this - you can even print it off to keep in the kitchen! Alternatively, you can use the touch test. Rare steak feels soft and spongy, medium rare is very slightly springy, and well-done steak will feel firm to the touch.