This article is from the Cooking and Conversions FAQ, by with numerous contributions by Victor Sack cooking.faq@mac.com others.
If you don't have unsweetened baking chocolate, substitute three
tablespoons of unsweetened cocoa powder plus one tablespoon of fat
(preferably oil) for each one ounce square.
US dark chocolate is the same as UK plain chocolate, that is, the
darkest and least sweet of the chocolates intended for eating (also
called bittersweet). What is called milk chocolate in the UK is called
milk chocolate in the US, too, but many people simply refer to it as
"chocolate". The stuff called "semi-sweet chocolate" by some folks is
the US dark or UK plain. "Bitter chocolate" is, apparently, the UK term
for high quality plain chocolate.
Some manufacturers apparently distinguish between "sweet dark,"
"semi-sweet" and "bittersweet" (Sarotti is one), but they seem to be
minor variations on a theme.
Chocolate chips are not necessarily a substitute for bar chocolates,
because the chips have something added to them to slow down melting.
 
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