Actually they do. A stone is around 14 pounds. This is OK, but the measurement is not accurate enough so someone may say "I weigh 10 3/4 stone". If I was in charge I would modify this to boulders, rocks and pebbles where 4 pebbles=1 rock, 4 rocks=1 boulder and 4 boulders=1 stone. The same flaw exists with temp measurement in celsius. 28 deg C. is much warmer than 26 but it doesn't sound like much.