Calculating the right resistor for your LED circuit doesn’t have to be guesswork. This free LED resistor calculator instantly gives you the exact current-limiting resistor value, power dissipation, and groups-per-meter for your strip light project — using the standard Ohm’s Law formula.
Trên trang này
Use the Calculator
Enter your circuit values below. All fields are required. The calculator returns the recommended resistor, power per group, and groups per meter.
Máy tính điện trở LED
The Principle — Ohm’s Law
Every LED needs a current-limiting resistor to prevent it from burning out. The resistor drops the excess voltage from your power supply down to what the LED string actually needs. The formula is straightforward:
R = (Vcung cấp − Vf × N) / If
V.cung cấp
Your DC power supply voltage (e.g., 12V or 24V).
V.f
LED forward voltage (check datasheet — red ~2V, white/blue ~3V).
N
Number of LEDs in series per resistor group.
TÔIf
Forward current in Amperes (e.g., 20 mA = 0.02 A).
Nó hoạt động như thế nào
The calculator takes five inputs and runs the Ohm’s Law formula automatically:
1. Input Voltage
Supply voltage (12V, 24V, or custom).
2. LED Forward Voltage
V.f per LED from the strip datasheet.
3. Forward Current
Target current in mA (typically 18–20 mA).
4. LEDs per Group
How many LEDs share one resistor.
5. LEDs per Meter
Density of the strip (30, 60, 120, etc.).
Output
Resistor value, wattage, groups per meter, circuit diagram.
Worked Example
Let’s walk through a typical 12V strip light scenario:
Kịch bản: 12V supply, 3 red LEDs in series per group (2V each, 20 mA), 30 LEDs per meter.
Bước 1: Total LED voltage = 2V × 3 = 6V
Bước 2: Resistor = (12V − 6V) / 0.020 A = 300 Ω
Bước 3: Groups per meter = 30 / 3 = 10 groups
Step 4: Power per meter = 10 groups × (2V × 0.020A × 3) = 1.2 W/m
Important Design Notes
Practical guidance when using the calculator results in a real LED strip project:
Use standard resistor values
Round up to the nearest E24/E96 standard value. A slightly higher resistor reduces brightness marginally but keeps LEDs safe.
Check resistor wattage
Pick a resistor rated at least 2× the calculated power dissipation to avoid overheating.
LED color = Vf
Red ≈ 1.8–2.2V, green ≈ 2.8–3.2V, white/blue ≈ 3.0–3.4V. Always check the datasheet.
Driver vs resistor
For high-density strips (120+ LEDs/m), use a constant-current LED driver instead of resistors for efficiency and reliability.
Câu hỏi thường gặp
Why do LEDs need a resistor?
LEDs are diodes — their current rises exponentially with voltage. Without a current-limiting resistor, even a small voltage spike can push excessive current through the LED and destroy it instantly. The resistor keeps current at the rated safe value.
Can I use the same resistor for all LEDs on a strip?
Most commercial LED strips already have surface-mount resistors built into the PCB for each series group. You only need this calculator when designing a custom circuit, using bare LEDs, or modifying a strip. For ready-made strips, just use a matching dải đèn LED with the correct voltage.
What’s the difference between a resistor and a constant-current driver?
Resistors are simple and cheap but inefficient — they waste power as heat. Constant-current LED drivers regulate current electronically and are far more efficient, especially for high-power strips. See our guide on dimming LED strip lights for more on driver choices.
What if my calculated resistor value isn’t a standard value?
Always round up to the nearest standard E24 series value. A slightly higher resistor means slightly lower current (marginally dimmer), but it’s safe. Rounding down risks over-driving the LED. If you’re unsure, check our Câu hỏi thường gặp về đèn dải LED or contact our engineering team.
Need Help Designing Your LED Strip Circuit?
Lightstec’s engineering team can recommend the right strip, driver, and accessories for your project.