The Finger Test to Check the Doneness of Meat, by Elise on Simply Recipes
Raw:
Open the palm of your hand. Relax the hand. Take the index finger of
your other hand and push on the fleshy area between the thumb and the
base of the palm. Make sure your hand is relaxed. This is what raw
meat feels like. (Check this out the next time you have a raw steak to
cook.)
Welldone:
Now gently press the tip of your pinky and your thumb together. Again
feel the fleshy area below the thumb. It should feel quite firm. This
is what well done meat feels like when you press on it. (Check this
out the next time you overcook a piece of meat.)
Medium:
Press the tip of your ring finger and your thumb together. The flesh
beneath the thumb should give a little more. This is what meat cooked
to a medium doneness feels like.
Medium Rare:
Gently press the tip of your middle finger to the tip of your thumb.
This is medium rare.
Rare
Press the tip of your index finger to the tip of your thumb. The
fleshy area below the thumb should give quite a bit. This is what meat
cooked to rare feels like. Open up your palm again and compare raw to
rare.
Sources: simplyrecipes.com
Illustration (unknown origin).

Sources: simplyrecipes.com