Both voltmeter and ammeter are electrical instruments used to detect two different parameters in an electric circuit. Purpose of voltmeter is to detect potential difference between two points in an electrical or electronic circuit; whereas, ammeter is used to quantitatively measure flow of current through a closed circuit. Analog version of both of them can be practically created from a galvanometer. Galvanometer is an electro-mechanical instrument used to detect presence or absence of current in an electric circuit. When a very high resistance is attached in series with the galvanometer, it acts like a voltmeter. On the other hand, when a small resistance is attached in parallel with the galvanometer, it behaves like an ammeter. Basic similarities and differences between voltmeter and ammeter are discussed in the following sections.

Similarities between voltmeter and ammeter

• Voltmeter and ammeter are electrical instruments and need electricity as well as complete electric circuit to display readings.
• A galvanometer can be converted to any of them.

Difference between voltmeter and ammeter

Voltmeter	Ammeter
Voltmeter is an instrument used to measure potential difference (in volt) between two points in an electrical circuit.	Ammeter is an instrument used to measure electric current (in ampere) flowing through a cable in an electrical circuit.
Internal electrical resistance of a voltmeter should be very high. An ideal voltmeter has infinite resistance.	Internal electrical resistance of an ammeter should be very low. An ideal ammeter has zero resistance.
While measuring potential difference between two points, the voltmeter must be connected in parallel with those points.	While measuring flow of current between two points, the ammeter must be connected in series with those points.
In schematic representation of voltmeter, it is denoted by a circle with V inside it.	In schematic representation of ammeter, it is denoted by a circle with A inside it.
A voltmeter can be created by attaching a very high resistance in series with the galvanometer.	An ammeter can be created by attaching a small resistance in parallel with the galvanometer.