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Tools/LED Resistor Calculator

LED Resistor Calculator

Calculate the current-limiting resistor for any LED. Nearest E24 standard value included.

Component Values

V
V
mA

Results

Exact R value150 Ω
Nearest E24 standard150 Ω
Actual If (with E24 R)20.0 mA
Power dissipation (exact R)60.0 mW
Power dissipation (E24 R)60.0 mW
Recommended wattage1/8 W
+−5 V150 ΩVf = 2 V→ 20 mA

LED + Current-Limiting Resistor

How to calculate the LED resistor

An LED requires a current-limiting resistor to prevent excess current from destroying it. The resistor value is chosen so that the voltage drop across it equals Vcc minus the LED's forward voltage, at the desired forward current.

Nearest E24 standard

R = (Vcc − Vf) / If

Power dissipation (exact R)

P = If² × R

Key Points

  • Always use a standard E24/E12 value — exact values rarely exist
  • Size the resistor wattage at ≥2× the calculated power
  • Typical If for indication LEDs: 5–20 mA
  • High-brightness LEDs may require 30–350 mA

Typical Vf Values

  • Red / Orange / Yellow: 1.8–2.2 V
  • Green (standard): 2.0–2.5 V
  • Blue / White / Green (HB): 3.0–3.5 V
  • IR (850–950 nm): 1.0–1.5 V