## Resistor Value Calculation for LED

In this blog I am going teach you calculation for the value of resistor that is used in the protection of led. Currently LED’s ( Light Emitting Diodes ) are used for wide range of purpose mainly as indicators.

Light emitting diodes are very sensitive. They easily get blown off with a slight higher voltage or current, to protect them we should add a resistance in series.

So before I show you the calculations, you must know that every colour of LED has a specific voltage drop across its terminal.

**Now lets come to the calculation part**

The value of resistance can be easily calculated by **Ohm’s law**

**V ( Voltage ) = I ( Current ) x R ( Resistor )**

Here,

**Voltage = Source Voltage – Voltage drop by LED**

**Example**

Suppose we need to calculate the value of resistance for green LED

Then,

Source voltage = 9v ( Applied voltage )

Voltage drop by Green LED = 4 Volt

Current = 25mA = 0.025 Ampere ( This is the current consumed by LED )

R = ?

By Ohm’s law

Resistance = voltage / Current

Resistance = ( source voltage – Voltage drop by LED ) / Current consumed by LED

Resistance = (9 – 4) Volt / 0.025 Ampere

Resistance = 5 V / 0.025 A = **200 Ohm**

### Power of resistor

Power of resistor can be easily calculated by

**P ( Power ) = V ( Voltage ) x I ( Current )**

**P = ( Source voltage – Voltage drop by LED ) x I ( Current consumed by LED )**

P = 5Volt x 0.025 Ampere

**P = 0.125 W** ( power of resistor must be greater than this value )

Every value of resistor is not available in market so we go for the nearest value available.

**Resistor from market = 200 Ohm, 0.25 Watt**

### Frequently asked questions

**How to calculate resistance if two or more LED’s are connected in parallel ?**

- When two or more LED’s are connected in parallel. Voltage across parallel combination of LED remains constant and current gets added.
- For example, if there are two led of 4v and 25 mA each. The parallel combination of two led will consume 4v and 50mA.

**How to calculate resistance if two or more LED’s are connected in series ?**

- When two or more LED’s are connected in series. Current across the parallel combination remains the same and voltage gets added.
- For example, if there are three led of 4v and 25mA each. Then the series combination of three led will consume 12v and 25mA.

**Author**

Akash Sharma

**Learn more about electronics on my website –**

Great article. Thank you for sharing. I’m retired Aircraft mechanic but now learning the electronics side of things. I take most available courses and buy equipment as required. Will look at the articles on this page. Thanks for sharing Artie 😊

Thank you for your valuable comment. It means a lot to me.