About the LED Strip Power Calculator
This LED strip power calculator sizes the power supply for an LED tape installation. Enter the strip length, its rated watts per metre (printed on the reel or listed by the seller), the supply voltage and how bright you will run it, and it returns the total power, the current draw and a recommended power supply rating with headroom. It also estimates the voltage lost in the copper wire between the supply and the start of the strip.
It is meant for under-cabinet lighting, cove and shelf lighting, addressable WS2812B/SK6812 pixel strips, TV backlights and signage. Typical ratings are around 4.8 W/m for 60 LED/m 3528 tape, 14.4 W/m for 60 LED/m 5050 tape and up to about 18 W/m for 60 pixel/m addressable strips at full white.
The supply recommendation adds a headroom percentage (20% is common) so the supply runs cool and lasts longer. Voltage drop is calculated for the two-conductor feed run only, using copper resistance at 20 °C; the strip itself also loses voltage along its length, which is why long 5 V and 12 V runs need power injected at several points.
With the default inputs, the recommended power supply is 86.4 W. Change any value above to recalculate instantly.
How to use the led strip power calculator
- 1Measure the total strip length in metres.
- 2Read the watts-per-metre rating from the reel, label or product listing.
- 3Choose the strip voltage and the brightness you will run it at.
- 4Enter the feed wire length and gauge from the supply to the strip.
- 5Buy a power supply at least as large as the recommended rating.
Formula and method
LED strips are rated in watts per metre at full brightness, so total power is simply length times rating, scaled by the brightness or PWM duty you will run. Current is power divided by the strip voltage — the same 72 W draws 6 A at 12 V but 14.4 A at 5 V, which is why low-voltage strips need heavier wiring.
The recommended supply adds headroom so it never runs at 100% of its rating. Feed-wire voltage drop uses Ohm’s law on the round trip (positive and negative conductors, so twice the one-way length) with the resistance per metre of solid-equivalent copper of the chosen AWG: d = 0.127 mm × 92^((36 − AWG)/39) and R = ρ ÷ (πd²/4), with ρ = 1.724 × 10⁻⁸ Ω·m at 20 °C.
- P
- Strip power (W)
- V
- Strip supply voltage
- I
- Current (A)
- L_wire
- One-way feed wire length (m)
- R/m
- Resistance of one conductor per metre (Ω/m)
Worked examples
5 m of 12 V 5050 strip at 14.4 W/m
5 m × 14.4 W/m = 72 W, or 6 A at 12 V. Adding 20% headroom gives an 86.4 W (7.2 A) supply, so a 100 W unit is the next standard size. Through 3 m of 18 AWG feed wire (0.021 Ω/m per conductor) the round trip drops 6 × 6 × 0.02095 ≈ 0.75 V, more than 6% — use 14 AWG or a shorter run.
10 m of 24 V high-density strip at 80% brightness
10 m × 19.2 W/m × 0.8 = 153.6 W, which is 6.4 A at 24 V. With 20% headroom you need about 185 W (a 200 W supply). Five metres of 16 AWG feed wire drops about 0.84 V, 3.5% of the supply.
2 m of 5 V WS2812B pixels at full white
120 pixels at up to 0.3 W each draw 36 W, a hefty 7.2 A at 5 V. A supply of at least 8.64 A (a 10 A, 50 W unit) is recommended, and even 1 m of 18 AWG wire loses 0.3 V (6%), so keep 5 V feeds short and thick.
Frequently asked questions
How do I calculate the power supply for an LED strip?+
Multiply the strip length in metres by its watts per metre, then add 20% headroom. For example 5 m × 14.4 W/m = 72 W, so choose a supply of at least 86 W — in practice a 100 W unit.
How many amps does an LED strip draw?+
Divide the total watts by the strip voltage. 60 W of strip draws 5 A at 12 V, 2.5 A at 24 V, and 12 A at 5 V. Higher-voltage strips draw less current for the same light output.
Why is the end of my LED strip dimmer?+
The thin copper inside the strip and the feed wire both drop voltage as current flows, so LEDs at the far end receive less voltage. Feed power at both ends or every few metres, use thicker wire, or switch to a 24 V strip.
Is 12 V or 24 V LED strip better?+
For the same wattage, 24 V strip draws half the current, so voltage drop and wire size are much smaller and runs can be roughly twice as long between feeds. 12 V strips are more common and easier to power from batteries.
Do LED strips use full power when dimmed?+
No. PWM dimming reduces average current roughly in proportion to brightness, and addressable strips only draw full power when every LED shows bright white. Size the supply for the brightest setting you will use.