When you want use it as adjective to equate some thing equal in value, measure, force, effect, significance, etc. use equivalent to which is common:
Is $50 equivalent to about £30?
His silence is equivalent to an admission of guilt.
When used as noun you have choose an appropriate preposition to match the temporal meaning, as:
This word has no equivalent in French.
Find out the equivalent of 5km in miles
Get me some information on how to substitute equivalent for buttermilk