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LED Power Calculator

Calculate LED circuit power requirements and efficiency analysis, optimize circuit design

Circuit Parameters
Enter basic LED circuit parameters to calculate power requirements
LED power formula
LED power depends on forward voltage, operating current, and how LEDs are grouped in series and parallel strings.
Series string voltage = LED forward voltage × LEDs in series
Parallel current = LED current × parallel strings
LED power = string voltage × total current
Resistor power = (supply voltage - string voltage) × total current
Total power = LED power + resistor power
Efficiency = LED power / total power × 100%
Vf
LED forward voltage
Typical voltage drop across one LED at the selected operating current.
If
LED forward current
Target current through one LED or one series string.
Vs
Supply voltage
The available voltage from the power supply or driver.
How this LED power calculator works
Use this section to verify the electrical assumptions behind a strip, module, sign, or small custom LED circuit.
  1. Choose the wiring pattern: series, parallel, or mixed series-parallel strings.
  2. Calculate the voltage required by each LED string from forward voltage and series count.
  3. Calculate total current from LED current and the number of parallel strings.
  4. Estimate LED power and any resistor dissipation from the voltage headroom.
  5. Flag inefficient combinations where resistor losses are large compared with LED power.

Important notes

  • Leave power-supply headroom for startup, temperature drift, cable drop, and manufacturer tolerances.
  • Constant-current drivers are usually safer than simple resistor-only designs for high-power LEDs.
  • Thermal design matters: LEDs draw power as heat as well as light.
LED power examples
These examples show how wiring choices change voltage, current, and power supply sizing.

Small series indicator string

Ten red indicator LEDs are wired in series from a 24 V supply.

  • LED count: 10
  • Forward voltage: 2.0 V
  • Current: 20 mA
  • Supply: 24 V

LED power is about 0.40 W, with voltage headroom for current control.

Series wiring keeps current low, but the supply voltage must exceed the LED string voltage.

Parallel decorative LEDs

Twenty LEDs share the same low-voltage supply in parallel.

  • LED count: 20
  • Forward voltage: 3.2 V
  • Current: 20 mA

Total current is about 400 mA before driver losses.

Parallel strings increase supply current quickly and need current balancing.

Mixed LED module

A module uses 4 LEDs per string and 5 strings in parallel.

  • 4 LEDs in series
  • 5 parallel strings
  • Forward voltage: 3.0 V
  • Current: 60 mA

String voltage is about 12 V and total current is about 300 mA.

Mixed wiring is common because it balances voltage requirements and current draw.

LED power FAQ
Common electrical checks before choosing an LED driver or power supply.