LED Resistor Calculator
How big a series resistor an LED needs so it won't burn out — enter supply, LED color, and current to get the E24 standard value instantly.
What it does: Compute the series resistor for an LED to avoid burning it out.
When to use it: When lighting a single LED, making an indicator, or building your first board following a tutorial.
Disclaimer: This result is a reference estimate. For actual production, refer to the device datasheet / local regulations as authoritative.
MEANS With this standard resistor, the actual current is about —, ≤ your target, so the LED is safe.
Common cases pre-computed: browse LED resistor presets →
No history yet. Each calculation is automatically saved to this device.
Read the guide: LED current-limiting resistor: theory & sizing · LED forward voltage chart by color
How to use the LED resistor calculator
Get a result in three steps.
- 01
Enter supply voltage Vs
USB is usually 5V, two alkaline cells ≈ 3V. You can type a plain number or include a unit, e.g.
5,5V, or9vall work. - 02
Enter LED forward voltage Vf
Red ≈
2.0V, yellow-green ≈2.2V, blue/white ≈3.2V. Refer to the datasheet as authoritative; if unsure, start with the median value for the color from the reference table. - 03
Enter target current I
Ordinary indicator LEDs commonly use
20mA. Low-power or small LEDs can use5–10mA. Click Calculate to read the E24 standard value and recommended power rating.
LED color → forward voltage Vf reference
When you don't know what Vf to enter, take the median from this table first; refer to the datasheet as authoritative for the final value.
| Color | Vf reference range (V) | Suggested median (V) |
|---|---|---|
| Red | 1.8 – 2.2 | 2.0 |
| Orange | 1.9 – 2.3 | 2.1 |
| Yellow | 2.0 – 2.4 | 2.2 |
| Yellow-Green | 2.0 – 2.4 | 2.2 |
| Pure Green | 3.0 – 3.4 | 3.2 |
| Blue | 3.0 – 3.4 | 3.2 |
| White | 3.0 – 3.6 | 3.2 |
Reference ranges from a set of common 5mm indicator LED datasheets (Kingbright/Lite-On, etc.). For precise design, use the datasheet of your actual device.
Common questions, answered in 3 minutes
Does an LED always need a resistor?
An LED is a current-driven device — a slightly higher voltage makes the current spike and burn it out. Unless you use a constant-current driver IC, a series current-limiting resistor is the simplest, most reliable solution.
What if I don't know the forward voltage?
Take the median for the color from the "quick reference table" (e.g. 3.2V for blue/white) and the computed resistor will be close to the real requirement. For more accuracy, check the datasheet and look at the Vf-If curve at the typical operating point.
Why take an E24 standard value instead of using the computed resistor directly?
E24 (IEC 60063) is the set of standard resistances stocked on the market. A computed 700Ω is not actually available to buy; the resulting 750Ω is what is on the shelf, and we round up to guarantee the LED never exceeds the target current.
How do I choose the power rating?
This tool's "recommended power rating" is already taken at ≥ 2× the actual dissipation, leaving a safety margin. If the ambient temperature is high or you want a long lifespan, bump it up one more level.
What about multiple LEDs?
Identical LEDs in series: add up all the Vf values and use the sum as the Vf input. In parallel: each LED needs its own current-limiting resistor — never share one.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| E24 standard resistance table | 10 11 12 13 15 16 18 20 22 24 27 30 33 36 39 43 47 51 56 62 68 75 82 91 | IEC 60063:2015 (E-series of preferred numbers) |
| Resistance formula | R = (Vs − Vf) / I | Ohm's law |
| Dissipation formula | P = (Vs − Vf) × I | P = V × I |
| Rounding direction | round up (direction = up) | Guarantees actual current ≤ target, LED never over-current |
| Recommended power rating | ≥ 2 × actual dissipation | Engineering convention (2× safety factor) |
All calculations on this page are based on the E24 table from IEC 60063:2015 and call no external API. For real circuits, refer to the device datasheet as authoritative.