PangPang ToolsSupply 12 V; three LEDs at 2 V each; target current 20 mA
Resistor drop 6 V; resistance 300 Ω; dissipation 0.12 WThe LED string drops 3 × 2 = 6 V, leaving 6 V for the resistor. At 0.02 A, 6 ÷ 0.02 = 300 Ω.
Construction & Electrical
LED series resistor and power calculator
About this tool
A series resistor can limit current in a small low-voltage DC LED circuit. The calculator subtracts the total LED forward voltage from the supply voltage, divides the remainder by the target current in amperes to obtain resistance, and multiplies drop by current to estimate resistor heat dissipation. It expects a positive voltage across the resistor. This simplified method is for low-power LED strings, not mains-powered luminaires or high-power LED drivers.
Resistors & LED circuits
Choose a task. Inputs stay in this page only.
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Result
Worked examples
Supply 9 V; two LEDs at 2 V each; target current 10 mA
Resistor drop 5 V; resistance 500 Ω; dissipation 0.05 W9 − 4 = 5 V across the resistor; 5 ÷ 0.01 = 500 Ω and 5 × 0.01 = 0.05 W.
Questions & answers
Is calculated dissipation the same as the resistor's required rating?
No. It is the expected operating heat dissipation under the entered assumptions. Select a resistor rated above it, allowing for ambient temperature and tolerances.
Can I use this for an AC mains lamp or a high-power LED?
No. Mains circuits need an appropriately certified driver and electrical safety design; high-power LEDs often require regulated constant-current drivers.
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Result
Worked examples
R1 resistance (Ω): 100, R2 resistance (Ω): 200
Series resistance: 300 ΩUsing these sample input values gives the first labelled output above. Ideal resistors; tolerance, thermal limits and frequency response are not included.
Questions & answers
Can I use the default numbers for purchasing or safety certification?
No. Replace the examples with your real values. Ideal resistors; tolerance, thermal limits and frequency response are not included.
MAKE IT SIMPLE
Result
Worked examples
Input voltage (V): 12, Upper resistor (Ω): 1000, Lower resistor (Ω): 2000
Divider output: 8 VUsing these sample input values gives the first labelled output above. No-load DC divider; attached load changes the output voltage.
Questions & answers
Can I use the default numbers for purchasing or safety certification?
No. Replace the examples with your real values. No-load DC divider; attached load changes the output voltage.