If you don't have a "beefy" bathroom scale like Bill, here's a trick for measuring your tongue weight at home. Divide the load half-and-half using a lever.
Get a 2 by 4 about 2 feet long, lay it on its narrow side for strength (the lever). Get 2 more short pieces of 2 by 4 about 6 inches long. Put the bathroom scale under one end of the lever, with one of the short pieces laying flat between the top of the scale and the lever (to spread the load). Under the other side of the lever lay the other short piece and then whatever you can find that will stand as tall as the bathroom scale. Now you can rest the tongue on the middle of the lever and the weight will be divided between the scale and the other side. Multiply whatever reading you get from the scale by 2.