LED Resistor Calculator

An LED needs a resistor in series because its current climbs almost vertically once the forward voltage is reached, and the resistor is what makes that current predictable. Enter the supply voltage, the forward voltage and the forward current from the datasheet and the tool returns the exact resistance, the nearest E12 and E24 standard values above it, the current those actually give and the power the resistor has to handle. Series strings and parallel strings are both covered, each parallel string with its own resistor, and a third tab runs it backwards for a resistor you already have. Forward voltage is a property of the part rather than a constant, so the current you measure will differ a little from the one you asked for.

Calculator Type

One LED and one resistor from a fixed supply.

From the datasheet for your part. As a rough guide only: red about 1.8 to 2.2 V, yellow and amber about 2.0 to 2.2 V, older green about 2.1 V, blue, white and modern green about 3.0 to 3.4 V, infrared about 1.2 to 1.6 V. These shift with current and temperature and vary between parts on the same reel.
From the datasheet. A standard 5 mm indicator LED is commonly run at 20 mA or less; the absolute maximum on the datasheet is a limit, not a target.
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Several LEDs in series make one string; several strings in parallel each need their own resistor. Never hang parallel LEDs off one shared resistor.

From the datasheet for your part. As a rough guide only: red about 1.8 to 2.2 V, yellow and amber about 2.0 to 2.2 V, older green about 2.1 V, blue, white and modern green about 3.0 to 3.4 V, infrared about 1.2 to 1.6 V. These shift with current and temperature and vary between parts on the same reel.
From the datasheet. A standard 5 mm indicator LED is commonly run at 20 mA or less; the absolute maximum on the datasheet is a limit, not a target.
Each string gets its own resistor.
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The other direction: a resistor already in the circuit, and what current it actually lets through.

From the datasheet for your part. As a rough guide only: red about 1.8 to 2.2 V, yellow and amber about 2.0 to 2.2 V, older green about 2.1 V, blue, white and modern green about 3.0 to 3.4 V, infrared about 1.2 to 1.6 V. These shift with current and temperature and vary between parts on the same reel.
The datasheet figure to compare against.
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