This simple and inexpensive device (a commercial one will cost you $97) will measure your hand gripping strength. It is made from 4 components: a fuel pump pressure gauge, a rubber tube, a tubing connector and a plastic water bottle.
To use just squeeze the water bottle and note the psi reading on the gauge. Then in my case I multiply the reading times 20 (about the square inches of my hand) to get pounds.
Grip squeeze pressure is a good indicator of physical health and you can compare your strength with others and yourself over time.
The great news is that you can buy everything you need to make one of these at Harbor Freight for 15 bucks: their cheapest fuel pressure gauge kit has the gauge, the tube, and the connector - all you need is a bottle and a hot glue gun.
By the way, my grip is about 7 psi (20 * 7 = 140 pounds).
Step 1: Insert Tubing Connector Into Bottle Cap
Drill a quarter inch hole in the bottle cap. Insert the quarter inch tubing connector (you can buy one at Home Depot for 99 cents) into the hole and glue using glue gun on both sides.
Step 2: Connect All the Parts
Attach the quarter inch hose to the pump and the bottle top tubing connector with clamps.
Screw on water bottle and squeeze.