Results

Exact Resistor Value

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Ω

Nearest E24 Standard

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Ω (E24)

Color Bands

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Power (Resistor)

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mW

Voltage Drop (R)

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V

Actual Current*

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mA

Resistor Rating

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W min

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*Actual current uses nearest E24 resistor. Always use a resistor with at least 2× the minimum power rating.

Common LED Specifications

LED Colour	Forward Voltage (Vf)	Typical Current (If)	Notes
Red	1.8 – 2.2 V	10 – 20 mA	Most common, lowest Vf
Orange / Amber	2.0 – 2.2 V	10 – 20 mA	Traffic lights, indicators
Yellow	2.0 – 2.2 V	10 – 20 mA	Similar to orange
Green (standard)	2.0 – 2.4 V	10 – 20 mA	Standard green (not bright green)
Green (bright)	3.0 – 3.4 V	10 – 20 mA	High-efficiency GaN-based
Blue	3.0 – 3.6 V	10 – 20 mA	Higher Vf — check supply voltage
White	3.0 – 3.6 V	10 – 20 mA	Blue die with phosphor — same as blue
UV	3.1 – 3.8 V	5 – 20 mA	UV-A (365–400nm)
Infrared (IR)	1.2 – 1.7 V	20 – 100 mA	Remote controls, sensors

Frequently Asked Questions

An LED is a diode — once its forward voltage (Vf) is exceeded, current increases exponentially with tiny voltage changes. Without a current-limiting resistor, a small increase in supply voltage leads to massively increased current, quickly burning out the LED. The resistor drops the excess voltage and limits current to a safe level, typically 10–20 mA for standard 5mm LEDs.

R = (Vs − Vf) / If, where Vs is supply voltage, Vf is LED forward voltage, and If is desired current in amps. For example: Vs = 5V, Vf = 2V, If = 20mA → R = (5 − 2) / 0.020 = 150Ω. For multiple LEDs in series, subtract the total Vf: R = (Vs − n × Vf) / If.

Power dissipated in the resistor = I² × R (or (Vs − Vf) × If). Always use a resistor rated at at least 2× this calculated power for safety margin. For most low-power LED circuits with 5–12V supply and 10–20mA current, 1/4W (0.25W) resistors are sufficient. For higher current LEDs or 12V+ circuits, use 1/2W or 1W resistors.

Resistors are manufactured in standard values from the E-series (E12, E24, E48, E96). E24 provides 24 values per decade (e.g., 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91 Ω, then repeating × 10). Most hobby and general electronics use E24. The nearest E24 value is often close enough — the LED will still work safely at a slightly different current.

Related Calculators

Understanding LED Circuits

When connecting an LED to a power supply, the current-limiting resistor is the most important component. LEDs have a characteristic I-V (current-voltage) curve that rises steeply — even 0.1V above the forward voltage can double the current. This is why LEDs cannot be connected directly to a voltage source: without current limiting, they fail in milliseconds.

Multiple LEDs in Series vs Parallel

LEDs in series share the same current — one resistor limits current for all. Total Vf = sum of individual Vf values. Make sure Vs > total Vf with enough headroom for the resistor. LEDs in parallel need individual resistors (never share a single resistor across parallel LEDs) because small Vf differences cause unequal current distribution. For large arrays, use a constant-current driver IC rather than resistors.