About the LED Strip Power Calculator
LED strips are sold by the metre and rated in watts per metre, but the power supply must be big enough for the whole length. This calculator takes the length of the strip, the power per metre and the voltage, and gives the total power, the current, the size of power supply to buy (with a safety margin) and how many separate feeds you need, because long runs at 12 volts dim at the far end. Type the strip length, the watts per metre and the voltage and the LED strip power appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the LED Strip Power Calculator
- 1Enter the strip length, the watts per metre and the voltage.
- 2Pick the units or options from the menus if the LED strip power tool offers them.
- 3Read the LED strip power in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the LED strip power
Makers, shop fitters and home owners use it to plan under-cabinet lighting, shelves, signs and stage lights. A power supply that is too small overheats or switches off, and one that is far too big wastes money.
Running a strip at 24 volts halves the current for the same power, so thin wires carry it further with less loss and less dimming. Choose 24 V for long runs when you can.
How the LED strip power is worked out
Total watts = length × watts per metre. Current = watts ÷ volts. Power supply = total watts × 1.2, rounded up. Single runs are limited to about 5 m at 12 V and 10 m at 24 V. A 5 metre strip rated at 14.4 W per metre uses 72 W, which at 12 V draws 6 A. A 90 W supply gives a 25 percent margin. A 12 metre strip of 9.6 W per metre at 24 V needs 115.2 W and two feeds, since one run should not be longer than 10 m.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Power, amps and supply size
- Run length limit
- 12 V and 24 V
Mistakes to avoid with LED strip power
The longest-run figures are common rules for ordinary strips and thin copper tracks; the real limit depends on the strip and the wire. Connect the power at both ends or feed long strips at several points. Always use a supply with the same voltage as the strip, and check the manufacturer's data.
On phone and computer
On a phone, type into the boxes one after another and read the LED strip power underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the LED strip power move. The led strip power calculator works the same on both. A long strip loses voltage along its length, so check that too. Use the Voltage Drop Calculator for long runs, the Watts to Amps Calculator for the supply current, and the Wire Gauge Calculator to choose a cable that handles it.
Features
- Add a 20% margin
- 24 V suits long runs
- Feed from both ends
- Clear messages when the LED strip power inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate LED strip power?
Total watts = length × watts per metre. Current = watts ÷ volts. Power supply = total watts × 1.2, rounded up. Single runs are limited to about 5 m at 12 V and 10 m at 24 V. A 5 metre strip rated at 14.4 W per metre uses 72 W, which at 12 V draws 6 A. A 90 W supply gives a 25 percent margin. A 12 metre strip of 9.6 W per metre at 24 V needs 115.2 W and two feeds, since one run should not be longer than 10 m.
What is the formula for LED strip power?
Total watts = length × watts per metre. Current = watts ÷ volts. Power supply = total watts × 1.2, rounded up. Single runs are limited to about 5 m at 12 V and 10 m at 24 V. The led strip power calculator applies it exactly and rounds only the displayed answer to six significant figures.
Why does a long strip get dimmer at the end?
Voltage is lost along the thin copper tracks of the strip, so the far end receives less than the supply gives.
How much margin should the power supply have?
About 20 percent over the load, which keeps it cool and helps it last.
Can I cut an LED strip?
Most strips have marked cutting points, often every 3 LEDs or 5 cm.
Is this led strip power calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.