Free tool
Steam ID Finder
One ID, four formats. Handy when a trade bot asks for one and your profile shows another.
Works with SteamID64, SteamID3, SteamID2, a profile link, or a raw account ID.
SteamID64
76561198000000000
SteamID3
[U:1:39734272]
SteamID2
STEAM_0:0:19867136
Account ID
39734272