Ampere or ‘amp’ is a unit of electric current denoted by A. The rate of electron flow in an electrical conductor is measured in Ampere.

One ampere of current represents one coulomb of electrical charge, i.e. 6.24×1018 charge carriers, moving in one second.

It is one of the seven basic SI units. It is named after a French Physicist and Mathematician Andre-Marie Ampere, who is considered as the ‘Father of Electrodynamics’.

Current is a count of a number of electrons that flows through a circuit. An ampere is the amount of produced by force of one volt acting through the resistance of one ohm. The ampere is nearly equal to one coulomb per second. As mentioned earlier, ampere helps to express the rate of flow of electrical charge. In any given point experiencing a current, if the charge on particles moving through it increases, the ampere value will increase proportionately.

It is to be noted that, ampere and Coulomb are two different units. Coulomb is also called as Ampere – second or Ampere – hour. As per SI units, constant and average current are expressed in Amperes.

1 A = 1 C/s

History of Ampere

The original definition of Ampere was different. It used to be one-tenth of the unit of electric current in centimeter – gram – second system of units. Now, those units are called abampere, which is defined as the amount of current that produces a force of two dynes per centimeter of length in between two wires that are at a one-centimeter distance.

Table of Ampere Unit Prefixes

Name Symbol Conversion Example
microampere(microamps) A 1A = 10-6A I = 40A
milliampere(milliamps) mA 1mA =  10-3A I = 2mA
ampere (amps) A I = 20A
kiloampere(kiloamps) kA 1kA = 103 I = 4kA

Conversion of amps(A) to kiloamps(kA):

One kiloamps (kA) is equal to thousand amps (A).

1 kA = 1000 A or 1 × 103  A

For example, 5 amperes of current can be converted to kiloamperes as follows:

5 A × 1000 = 5000 A or 5 kA

Conversion amps(A) to milliamps(mA):

One ampere is equal to 1000 milliamperes.

1 A = 1000 mA


1 mA = 0.001 A or 10-3 A

For example, 2 A to milliampere is converted as follows:

2 A/1000 = 0.002 A or 2 × 10-3 A = 2 mA

Conversion of amps(A) to microamps(A):

One ampere is equal to 1000000 or 10-6 microamperes.

1 A = 1000000 μA or 10-6  μA

For example, 5 A is converted to microamps as follows:

5 A / 1000000  = 0.000005 A or 5 × 10-6  A = 5 μA

Relationship Between Current And Voltage

Amps can be calculated using volts (V), watts (W) and ohms (Ω) but you cannot convert these units to amps as these represent different quantities.

Volts to amps calculation with watts

We know that power of a circuit can be calculated using the following formula

P (W) = V (V) × I (A)

Now, current from the above equation can be calculated as follows:

I (A) = P (W) / V (V)

For example, what is the current flow in a circuit that consumes 50 W of power and has a supply voltage of 10 V?

Using the equation, we can calculate current as follows:

I (A) = 50 W/10 V = 5 A

Volts to amps calculation with ohms

We know that a resistance of a circuit can be calculated using the following formula:

V (V) = I(A) × R (Ω)

The current from the above equation can be calculated as follows:

I (A) = V (V) / R (Ω)

For example, the current in a circuit having a voltage of 25 V with a resistance of 5 Ω can be calculated as follows:

     I = 25 V/5 Ω = 5 A

Ampere Meter

Ampere meter, commonly known as Ammeter is an electrical instrument used to measure electrical current in Amperes. Electrical current on the load is measured with the help of Ampere meter by connecting it in series to the load. It has zero resistance and so measured circuit remains unaffected.


The ammeter cannot be connected in parallel to the load because of its low resistance. If it is connected in parallel it becomes a short circuit path allowing all the current to flow through it which may be lead to the burning of meter due to the high value of current. An ideal ammeter has zero impedance so that the power loss in the instrument is zero. But this ideal condition is not achievable practically.

Types of Ammeter

The classification of ammeter is based on the construction design and the type of current that flows through the ammeter. Based on the design of construction it is classified as follows:

  • Moving iron ammeter
  • Rectifier type ammeter
  • Permanent moving coil ammeter
  • Electro-dynamometer ammeter

Based on the type of current that flows through it, it is classified as follows:

  • DC ammeter
  • AC ammeter

The DC ammeters are mostly permanent moving coil type ammeter. The other types of ammeter can measure both AC and DC current.

Stay tuned with Byju’s to learn more about ampere law, electric current and much more.

Practise This Question

What will be the self inductance of a coil, to be connected in a series with a  resistance of π3Ω such that the phase difference between the emf and the current at 50 Hz frequency is 30