How to determine the wire size for LED lights

Updated February 21, 2017

Light emitting diodes (LEDs) are efficient, power-saving lights that last years. Most of the electricity an LED light consumes is converted into light, unlike regular light bulbs, where a lot of energy is lost as heat. It's important that you use the correct wire size for your LED lights, as a wire that's too thick has greater resistance, reducing the effectiveness of a light that requires such a small amount of electrical energy.

Work out how many LED lights you intend to wire. Look on one of the LED lights to ascertain the amperes. The amperes are likely to be measured in milliamp hours (mAh) because LEDs use very little power.

Multiply the mAh that one LED uses by the number of LEDs you're wiring. For example, if one LED uses 250 mAh and you are using 20 then multiply 250 by 20 to get 5,000 mAh. To get the amperes, divide the figure by 1,000, which will give you 5 amperes. You need to do this with whatever wiring method you have chosen. Write down the result.

Use a tape measure to measure the length of the wire you intend to use. You need to do this from the last LED you are wiring to the power supply. Double the result: If the distance is 20 feet, you need 40 feet of wire. Make a note of the result.

Navigate to the wire gauge table at You will see a table with a yellow line across the top and a green column down the left side. The top row refers to amperes the side column refers to wire distance.

Refer to the amperes figure you made a note of earlier. Look at the yellow row and find the corresponding amperes. If there's not an exact match, use the next highest number.

Refer to the wire distance you made a note of earlier. Look at the green column and find the corresponding number. Use the next highest number if there's not an exact match.

Follow the amperes column down and the distance row across until they meet. The wire gauge size you need is in the white box.

Things You'll Need

  • Calculator
  • Tape measure
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About the Author

James Stevens has been writing articles for market research companies in the U.K. since 1990. He has written various country profiles for inclusion in comprehensive market reports including Vision One Research and Investzoom Market Research. Stevens holds a General Certificate of Education from Chelmsford College of Further Education.