Led resistor calculator

Series resistance = (supply voltage − LED forward voltage) ÷ current. Current in milliamps is divided by 1,000.

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Supply voltage (V)

LED forward voltage (V)

More inputs and assumptions

Target LED current (mA)

Answer

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Series resistance = (supply voltage − LED forward voltage) ÷ current. Current in milliamps is divided by 1,000.

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Precision and calculation record

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Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

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Formula and assumptions

This is an ideal single-LED circuit calculation. Select a real resistor and suitable power rating using component specifications and tolerances; the result is not a standard resistor recommendation.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Led resistor calculator

Series resistance = (supply voltage − LED forward voltage) ÷ current. Current in milliamps is divided by 1,000.

This is an ideal single-LED circuit calculation. Select a real resistor and suitable power rating using component specifications and tolerances; the result is not a standard resistor recommendation.

Next: Basic calculator

A worked example

With supply voltage (v) = 5, led forward voltage (v) = 2, target led current (ma) = 20, the calculated resistance (ohms) is 150.

Before you use the result

This is an ideal single-LED circuit calculation. Select a real resistor and suitable power rating using component specifications and tolerances; the result is not a standard resistor recommendation.

Example results for supply voltage (v)

These examples use LED forward voltage (V): 2; Target LED current (mA): 20. They are reference calculations, not recommended settings.

Supply voltage (V)	Calculated resistance (ohms)
2.5	25
5	150
10	400

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