Sake labels sometimes say “甘口 (amakuchi)” or “辛口 (karakuchi)”. Amakuchi is sake in which you easily taste sweetness, and karakuchi is sake in which you taste less sweetness. “Karakuchi” for sake corresponds to “dry” in English.
Nihonshu-do and san-do
The back label sometimes shows figures for “nihonshu-do (日本酒度, sake meter value)” and “san-do (酸度, acidity)”. Some sake does not show them.
Nihonshu-do is a number that shows how heavy a sake is compared with water. Sake lighter than water has a plus value, and sake heavier than water has a minus value. Sugar makes sake heavier, so the less sugar a sake has, the more it moves to the plus side, and the more sugar it has, the more it moves to the minus side. Most sake on the market is between plus 10 and minus 10.
San-do is a number that shows the amount of acid in a sake. When the san-do is high, the taste feels richer, the sweetness is hidden, and the sake tastes drier.
Nihonshu-do alone does not decide it
Nihonshu-do also changes with the alcohol content. More alcohol makes a sake lighter, so its nihonshu-do moves to the plus side. Also, even with the same amount of sugar, sake with more acid tastes drier. Whether a sake is amakuchi or karakuchi is decided by the balance of sugar and acid, so nihonshu-do alone does not decide it.
There is also an index called “amakara-do (甘辛度, sweet-dry index)”, calculated from the amount of sugar (glucose) and the san-do.