What values do I need?

Use the supply voltage, LED forward voltage from the datasheet or color preset, target forward current and the number of LEDs in series.

Can one resistor feed parallel LEDs?

Avoid a single shared resistor for parallel LEDs. Each branch should have its own current limiting, because forward voltage varies between parts.

What wattage resistor should I use?

Select a resistor with a power rating comfortably above the calculated dissipation, commonly with at least 2x margin for small hobby circuits.

LED Resistor Calculator

Calculate the series resistor and resistor wattage for one or more LEDs from supply voltage, forward voltage and target current.

LED resistor parameters

Supply voltage V_s, V

LED color / type

LED forward voltage V_f, V

LED forward current I_f, mA

Number of LEDs in series

Current-limiting resistor for LEDs

English SERP competitors focus on a practical electronics workflow: supply voltage, LED forward voltage, forward current and how many identical LEDs are in series.

R = \frac{V _{s} - n V _{f}}{I _{f}}

Vs is supply voltage, Vf LED forward voltage, n LED count and If target current.

P_{R} = I_{f}^{2} R

Choose a resistor package rated above the calculated dissipation.

LED driver caveat

Check the datasheet

Forward voltage and current vary by LED. High-power LEDs and LED strips often need a constant-current driver instead of a simple resistor.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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