LED Power Calculator
This LED Power Calculator estimates LED electrical power, supply power, resistor loss, voltage headroom, efficiency, and total array power for common LED circuits.
Use Single LED mode for one indicator, LED Series String mode for multiple LEDs in series, and LED Array mode for repeated parallel strings.
Engineering tool
LED Power Calculator
Calculate LED power, supply power, circuit loss, voltage headroom, and total array power for practical LED circuits.
Voltage applied to the LED circuit.
Forward voltage of one LED at the selected current.
Operating current through one LED or one string.
LED power
40 mW
Result console
- LED power
- 40mW
- Supply power
- 100mW
- Power loss
- 60mW
- LED efficiency
- 40%
Power level looks reasonable for a resistor-limited LED circuit.
Formula reference
LED Power Formulas
Use volts, amperes, and watts in the equations. The calculator converts engineering units before applying the formulas.
Single LED: PLED = Vf × IfPSupply = Vs × IfPloss = PSupply - PLEDEfficiency = PLED / PSupply × 100%Series string: VLED = Vf × NseriesPLED = VLED × IfLED array: PLEDsingle = Vf × IfPstring = PLEDsingle × LEDsPerStringItotal = If × ParallelStringsPLEDtotal = Pstring × ParallelStringsPSupply = Vs × ItotalVariable definitions
- Vs
- Supply voltage
- Vf
- Forward voltage of one LED
- If
- LED current or string current
- Nseries
- LEDs connected in series
- Nparallel
- Parallel LED strings
- PLED
- Electrical LED power
Variable Definitions
- Supply voltage
- The voltage source feeding the LED circuit.
- LED forward voltage
- The voltage drop of one LED at the selected operating current.
- LED current
- Current through one LED or one series LED string.
- LEDs in series
- LEDs that share the same current and add forward voltage.
- Parallel strings
- Repeated LED strings that multiply total supply current.
- Power loss
- Supply power that is not consumed by the LEDs, usually dissipated as resistor heat.
Worked Example
Single LED
A 5 V supply drives one LED with 2 V forward voltage at 20 mA.
- LED power
- 40 mW
- Supply power
- 100 mW
- Power loss
- 60 mW
- Efficiency
- 40%
LED Array
A 12 V supply drives four parallel strings, each with three 3 V LEDs at 20 mA.
- Power per LED
- 60 mW
- Power per string
- 180 mW
- Total LED power
- 720 mW
- Total supply current
- 80 mA
- Total supply power
- 960 mW
Check current and thermal limits
LED power becomes heat and light. Verify current rating, package temperature, and board cooling.
Series strings improve efficiency
Using more LEDs in series can reduce resistor loss when enough supply voltage is available.
Parallel strings multiply current
Each parallel string should normally have its own current limiting resistor or driver channel.
Use constant-current drivers for high power
High-power LED designs usually need current regulation instead of a simple resistor.
Support reference
FAQ
How do you calculate LED power?
LED power is the LED forward voltage multiplied by LED current: PLED = Vf × If.
What is supply power in an LED circuit?
Supply power is the supply voltage multiplied by the total supply current. It includes LED power and power lost in the current-limiting element.
Why is LED circuit efficiency below 100%?
A resistor-limited LED circuit dissipates unused voltage as heat in the resistor, so supply power is greater than LED optical/electrical load power.
How do series LEDs affect power?
Series LEDs add their forward voltages while sharing the same current. Total LED power is the total LED voltage multiplied by the string current.
How do parallel LED strings affect supply current?
Parallel strings multiply supply current. If each string uses 20 mA and there are four strings, total supply current is 80 mA.
Can this calculator size resistor wattage?
It estimates circuit loss and power headroom. For resistor wattage selection, also use the LED Current Calculator or LED Resistor Calculator.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Blog
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Engineering Disclaimer
This calculator provides first-order electrical estimates for LED power circuits. Verify LED datasheet limits, resistor dissipation, driver capability, PCB temperature, and supply tolerance before production use.