Voltage Drop & Wire Calculator

Understanding Voltage Drop in LED Strip Installations

Voltage drop is one of the most misunderstood aspects of LED installation design. Every length of wire and every metre of LED strip copper trace introduces resistance. When current flows through that resistance, a fraction of the supply voltage is lost as heat. At the far end of a long strip, the voltage that actually reaches the LEDs can be meaningfully lower than what your power supply is providing at the input.

For 5V LED strips, this is particularly critical. WS2812B LEDs operate correctly between 4.5V and 5.5V. A voltage drop of even 0.5V can cause colour inaccuracy — LEDs at the far end of a long strip will appear dimmer and often show a warm colour cast because the red LED channel (which has the lowest forward voltage) continues to operate while the blue and green channels begin to drop out. On 12V strips, the proportional impact of the same ohmic drop is smaller, which is one reason 12V strips are preferred for longer runs.

How Voltage Drop Is Calculated

Ohm's Law and Wire Resistance

Voltage drop across a wire is calculated using V = I × R, where I is the current in amps and R is the wire resistance in ohms. Wire resistance depends on the conductor material (copper), the cross-sectional area (determined by AWG gauge), and the length of the run. For a wire run, you must count both the positive and negative conductors — current flows out and back, so a 3-metre wire run has 6 metres of effective conductor length.

LED Strip Trace Resistance

The copper traces within the LED strip itself also have resistance. This is in addition to the feed wire resistance. A typical 5V 60 LED/m strip has approximately 0.3–0.5 ohms per metre of strip. This means that even with thick feed wire, a 5-metre strip will still experience voltage drop along its own length. The calculator models both the feed wire and the strip trace resistance to give you the voltage at the strip midpoint and far end.

Power Injection

Power injection means adding additional power supply connections at intermediate points along the strip. Instead of power only entering at one end, you feed 5V in at both ends, or every 2–3 metres for very long runs. This halves or thirds the effective current each section of strip trace must carry, dramatically reducing the voltage drop. The Voltage Drop Calculator tells you precisely where to add injection points.

Signs You Have Voltage Drop Problems

• • LEDs at the far end of the strip appear dimmer than those near the power injection point.
• • White effects appear warm or yellow-orange toward the end of the strip (blue channel dropping out first).
• • Colour effects look different at the start and end of the strip.
• • The first few LEDs near the power connection are much brighter than the rest.
• • Effects that should be symmetrical look uneven left-to-right.

How to Fix Voltage Drop

• • Add power injection at the far end of the strip — connect positive and ground from the PSU to the end of the strip as well as the beginning.
• • Use thicker wire (lower AWG number) between the PSU and the strip.
• • Reduce the length of individual strip segments and power each one separately.
• • Switch to a 12V strip type for long runs — the same wattage at 12V draws one-third the current, reducing resistive drop proportionally.
• • Reduce overall brightness using WLED's global brightness control — lower current means lower voltage drop.

Frequently Asked Questions