Electrical calculators
Works in your browser. Nothing is uploaded.LED resistor
Find the resistor an LED or a string of LEDs needs, the standard value to buy and its power rating.
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Color bands–
V
V
mA
Resistor to use
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Exact
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Current with it
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Heat in it
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Power rating, at least
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The next standard value up, from the E24 series, so the current stays at or below what you typed.The supply must be higher than the LEDs’ voltages added up.
Electrical calculators
Resistor color codeBands to ohms and back.Ohm’s law and powerVolts, amps, ohms and wattsVoltage drop and cable sizeThe drop over a run, and the smallest cable within itWire sizesAWG, mm², kcmil and diameterLED resistorThe resistor an LED needsSMD codesResistor and capacitor markings555 timerAstable and monostableBattery runtimeHow long a battery lasts
How to use it
- Type the supply
The voltage feeding the LEDs, such as 5 V, 12 V or a 9 V battery.
- Add the LEDs
Their forward voltage and current from the datasheet, and how many are in series.
- Buy the part
The standard value, the power rating to ask for and the color bands to look for.
Tips
- Typical LED voltages
Red and yellow LEDs drop about 2 V, blue and white about 3 V. The datasheet has the exact figure.
- Gentle current
Most small LEDs are bright at 5 to 10 mA, and they last longer below their maximum.
- One resistor each
LEDs side by side need a resistor each. Sharing one lets the brightest take most of the current.
In the app
Electrical calculator in Angle Meter
- LED strips and the power supply they need
- Resistor color code and SMD codes
- 555 timer, coils and RC circuits
- Series and parallel parts and dividers
Get it onGoogle PlayComing soon to the App Store
Electrical calculator guide ›