LED Resistor Calculator

How to Calculate an LED Resistor

Every LED needs a current limiting resistor (CLR) in series to prevent it from drawing too much current and burning out. The calculation uses Ohm’s law:

1. Find the voltage drop across the resistor. Subtract the LED’s forward voltage from your supply voltage: V_R = V_supply − V_f
2. Divide by the desired current. R = V_R / I. Make sure to use amps, not milliamps — divide mA by 1000 first.
3. Round up to a standard value. Pick the nearest E24 resistor value that is equal to or greater than the calculated resistance. This ensures the actual current is at or below your target.

Example: 9V supply, red LED (V_f = 2V), 15mA desired current. R = (9 − 2) / 0.015 = 467Ω. The nearest standard value is 470Ω.

LED Forward Voltage Reference

The forward voltage depends on the LED colour, which is determined by the semiconductor material. These are typical values — always check your specific LED’s datasheet for the exact figure.

LED Colour	Typical Vf	Range
Red	2.0V	1.8 – 2.2V
Orange	2.1V	2.0 – 2.2V
Yellow	2.1V	2.0 – 2.2V
Green (standard)	2.1V	2.0 – 2.2V
Green (bright / InGaN)	3.3V	3.0 – 3.5V
Blue	3.2V	3.0 – 3.4V
White	3.2V	3.0 – 3.4V
UV / Purple	3.3V	3.1 – 3.5V
Infrared	1.2V	1.0 – 1.5V

Choosing the Right Current for Pedal LEDs

Most standard 5mm LEDs are rated for a maximum of 20mA, but that doesn’t mean you should run them at full blast. For indicator LEDs in guitar pedals, lower currents are usually better:

• 10–15mA — standard brightness for indicator LEDs. This is the sweet spot for most builds.
• 2–5mA — if you’re using ultra-bright or high-efficiency LEDs. Modern LEDs are incredibly bright and often need less current than you’d expect.
• 1–2mA — dim enough for stage use without being distracting. Many builders prefer this for gigging.

Higher resistance = less current = dimmer LED. There’s no harm in going dimmer — many builders deliberately use 1kΩ to 4.7kΩ resistors for a subtle glow that won’t blind you on a dark stage.

LEDs in Series

When connecting multiple LEDs in series (cathode of one to anode of the next), they share the same current but each LED drops its own forward voltage. The resistor calculation becomes:

R = (Vsupply − (Vf1 + Vf2 + …)) / I

The total forward voltage of all LEDs combined must be less than the supply voltage, otherwise there won’t be enough voltage left for the resistor to regulate the current. For example, with a 9V supply you can run up to two blue LEDs in series (3.2V + 3.2V = 6.4V), but not three (9.6V exceeds the supply).

Power Dissipation and Resistor Wattage

The resistor converts excess voltage to heat. To find the power dissipated:

P = (Vsupply − Vf) × I

For a typical pedal indicator LED (9V, 2V LED, 15mA), the power is (9 − 2) × 0.015 = 0.105W. A standard ¼W (0.25W) resistor handles this easily. You’d need a ½W resistor only if the power exceeds 0.25W, which is rare in LED circuits at pedal voltages.

Once your indicator LED is sorted, use our resistor colour code calculator to identify the bands on your chosen resistor, then plan your enclosure layout with Stompbox Layout — place LED holes with millimetre precision and export print-ready drill templates.

Common CLR Values for Guitar Pedals

Here are the most commonly used LED resistor values in pedal builds, assuming a 9V supply and a standard red LED (V_f ≈ 2V):

Resistor	Current	Brightness	Notes
330Ω	~21mA	Maximum	At the LED’s rated limit — not recommended
470Ω	~15mA	Bright	Standard choice for clear visibility
1kΩ	~7mA	Medium	Good all-round choice, saves battery
2.2kΩ	~3.2mA	Moderate	Still clearly visible, lower power draw
4.7kΩ	~1.5mA	Dim	Subtle glow — great for stage use with bright LEDs
10kΩ	~0.7mA	Very dim	Only works with ultra-bright / high-efficiency LEDs

Frequently Asked Questions

What resistor do I need for an LED?

Use the formula R = (V_supply − V_forward) / I. For a typical indicator LED in a 9V guitar pedal (V_f = 2V, I = 15mA), the calculation is R = (9 − 2) / 0.015 = 467Ω. The nearest standard value is 470Ω.

What resistor for an LED on 9V?

For a standard red LED on 9V: R = (9V − 2V) / 15mA = 467Ω → use 470Ω. For a blue or white LED: R = (9V − 3.2V) / 15mA = 387Ω → use 390Ω. A 1kΩ–4.7kΩ resistor will also work if you want a dimmer indicator LED.

What is a current limiting resistor (CLR)?

A current limiting resistor is placed in series with an LED to restrict the current flowing through it. LEDs have a very low resistance once they reach their forward voltage, so without a resistor they would draw excessive current and burn out almost instantly. The CLR drops the excess voltage and sets the LED current to a safe level.

What is the forward voltage of an LED?

The forward voltage (V_f) is the minimum voltage needed across an LED for it to light up. It varies by colour: red LEDs are typically 1.8–2.2V, yellow and standard green are 2.0–2.2V, bright/InGaN green LEDs are 3.0–3.5V, and blue and white are 3.0–3.4V. Check your LED’s datasheet for the exact value.

Can I use a higher resistor value than calculated?

Yes. Using a higher resistor value will reduce the current and make the LED dimmer, but it won’t damage anything. Many pedal builders deliberately use higher values (1kΩ–4.7kΩ) for indicator LEDs to avoid blinding brightness and reduce current draw. Going lower than the calculated value risks overdriving the LED.

What wattage resistor do I need for an LED?

Calculate the power dissipation: P = (V_supply − V_forward) × I. For a typical pedal indicator LED (9V, 2V LED, 15mA), the power is about 0.1W. A standard ¼W (0.25W) resistor is more than sufficient for nearly all LED applications in guitar pedals. Use our resistor colour code calculator to verify the bands on the resistor you pick.