Technology
Resistive voltage divider
Find the unloaded output voltage of a two-resistor voltage divider.
Calculators / Technology / LED series resistor
LED series resistor calculator
Estimate a series resistor for one LED at a chosen current.
On this page
Calculated resistance150Ω
Resistor dissipation0.06W
Calculator controls
How to calculate
Estimate a series resistor for one LED at a chosen current.
Calculated resistance = (v-f)/(i/1000) Ω; Resistor dissipation = (v-f)*(i/1000) W
Worked example
Supply voltage (V): 5; LED forward voltage (V): 2; Target LED current (mA): 20.
Calculated resistance: 150 Ω; Resistor dissipation: 0.06 W.
Assumptions and limits
Uses ideal components and the units shown. This calculation does not establish component ratings, wiring safety or regulatory compliance. Select an appropriate standard resistor and separately check its power rating and the LED datasheet; forward voltage varies.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate a series resistor for one LED at a chosen current.
When this tool is useful
Calculated resistance = (v-f)/(i/1000) Ω; Resistor dissipation = (v-f)*(i/1000) W
Understanding your inputs
| Input | What to enter |
|---|---|
| Supply voltage (V) | Enter a number of at least 1e-12 and no more than 1000000000000. |
| LED forward voltage (V) | Enter a number of at least 0 and no more than 1000000000000. |
| Target LED current (mA) | Enter a number of at least 1e-12 and no more than 1000000000000. |
Frequently asked questions
What assumptions does this calculation use?
Uses ideal components and the units shown. This calculation does not establish component ratings, wiring safety or regulatory compliance. Select an appropriate standard resistor and separately check its power rating and the LED datasheet; forward voltage varies.
How is the result calculated?
Calculated resistance = (v-f)/(i/1000) Ω; Resistor dissipation = (v-f)*(i/1000) W