How to use the calculator
- Find the power per metre (or per foot) and the voltage on the strip’s datasheet or reel label.
- Enter the total length you will install and the headroom you want.
- If the datasheet gives a maximum run length per feed, enter it to see how many separate feed points the installation needs.
Formula
P = power per length × length | I = P ÷ V | supply rating = P × (1 + headroom ÷ 100)
Feed points = total length ÷ maximum run length, rounded up. These are the basic relations between power, voltage and current (P = V × I).
Why headroom?
Running a power supply continuously at its full rated output leaves no margin, and many supplies have to be derated at higher temperatures. A margin of around 20% is a common rule of thumb, which is why it is the default here; it is a convention rather than a standard. The datasheet of the power supply you choose is the authority on its continuous load and temperature derating.
Units
Power in watts (W), voltage in volts (V DC), current in amperes (A), length in metres or feet (the power per length must use the same unit).
Source
The calculation uses only the electrical relation P = V × I and the strip and supply figures you enter from their datasheets. No product data is built into the tool.
Limits and safety
- This calculator covers the low-voltage DC side only. Connecting a power supply to mains electricity is work for a qualified electrician and must follow the wiring rules where you live. Nothing on this page is wiring instructions.
- Long strips lose voltage along their length, which can make the far end dimmer. The maximum run length from the strip’s datasheet is the reference; this tool does not calculate voltage drop or wire sizes.
- RGB, RGBW and tunable-white strips may list power at full output of all channels. Use the figure from the datasheet for the highest setting you will use.
- Controllers, dimmers and amplifiers have their own current limits. Check those separately.