LED Resistor Calculator
Find the series resistor an LED needs from the supply voltage, the LED forward voltage and the target current. Enter supply voltage, led forward…
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Find the series resistor an LED needs from the supply voltage, the LED forward voltage and the target current. Enter supply voltage, led forward voltage and led current to see resistor needed and resistor power when you calculate.
Worked example
Example calculated from the starting values. Enter your own values and press Calculate to get your result.
With the default inputs (supply voltage = 12 V, LED forward voltage = 2 V, LED current = 20 mA), the results are: resistor needed 500 ohms; resistor power 0.200 W.
Quick reference: supply voltage vs result
Reference table based on the example values; it is not your calculation result.
| Supply voltage (V) | Resistor needed | Resistor power |
|---|---|---|
| 6 | 200 ohms | 0.080 W |
| 12 | 500 ohms | 0.200 W |
| 24 | 1,100 ohms | 0.440 W |
| 60 | 2,900 ohms | 1.160 W |
| 120 | 5,900 ohms | 2.360 W |
| 240 | 11,900 ohms | 4.760 W |
Frequently asked questions
What formula does this calculator use?
Resistor needed = (vs-vf) ÷ (i ÷ 1000); Resistor power = (vs-vf) × (i ÷ 1000). Variables: vs = supply voltage in V, vf = led forward voltage in V, i = led current in mA.
What do I need to enter?
You need supply voltage (V), led forward voltage (V), led current (mA). Results update as you type.
What is an example result?
With the default inputs (supply voltage = 12 V, LED forward voltage = 2 V, LED current = 20 mA), the results are: resistor needed 500 ohms; resistor power 0.200 W.
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