The resistance of an ideal ammeter is zero.
Voltmeter
A voltmeter is a high resistance galvanometer used for measuring the potential difference between two points. It is always connected in parallel.
The resistance of an ideal voltmeter is infinity. Conversion of a Galvanometer into a Voltmeter
A galvanometer can be converted into a voltmeter by connecting a high resistance into its series.
If a galvanometer of resistance G show full scale deflection for current Ig then required high resistance R, connected in series for converting it into a voltmeter of range V is given by