LED Resistor Calculator

Basic calculation with LED preset and target current

V_sup

Color Preset

V_f

LED Current

Typical: 3-20 mA for indicator LEDs

Adjust parameters to see results

Calculate the current-limiting resistor for a single LED with three calculation modes:

Simple Mode

Basic calculation with LED preset and target current. No tolerances, E12/E24 series only.

Advanced Mode

Full control with voltage/V_f tolerances, E-series selection, power margin, PWM.

Reverse Mode

Calculate LED current for given resistor. Useful for checking existing circuits.

Basic Calculation (Forward)

The nominal resistance is calculated from Ohm's law:

R_nom = (V_sup − V_f) / I_LED

Worst-Case Analysis

For each candidate resistor (or reverse calculation), LED current is computed across all corners:

I_min = (V_sup,min − V_f,max) / R

I_typ = (V_sup,typ − V_f,typ) / R

I_max = (V_sup,max − V_f,min) / R

Power Rating

Resistor power dissipation with safety margin (default 1.5×):

P_max = I_max² × R

P_rating = P_max × margin

V_{sup}

= Supply voltageV

V_f

= LED forward voltageV

I_{LED}

= LED currentmA

R

= Current-limiting resistanceΩ

P

= Power dissipationW

📘 Usage Notes

• Simple mode: Quick calculation for typical use cases (5V supply, standard LED)
• Advanced mode: Full worst-case analysis with tolerances and E-series selection
• Reverse mode: Check existing circuit — enter resistor value to see actual LED current
• LED presets are typical for indicator LEDs at 3 mA; always verify with datasheet
• For power LEDs (>100 mA), use Custom preset and consult manufacturer specs
• Results update automatically as you type (500ms debounce)
• Package recommendations: 0402 (1/16W) to 2512 (1W) for SMD resistors