How do I work out the total power of an LED strip?

Multiply the strip rating in watts per metre by the run length in metres. A 14.4 W/m strip over a 5 metre reel draws 14.4 × 5 = 72 W. That figure is the load before any supply headroom, so it is also the number you compare against a power brick rating. If you join two reels end to end, add their lengths first, then multiply once.

How much current does the strip pull, and why does it matter?

Current is power divided by voltage: I = P / V. The same 72 W load pulls 72 ÷ 12 = 6 A on a 12 V strip but only 72 ÷ 24 = 3 A on a 24 V one. Current matters because the wire gauge, the connector rating and the voltage drop along the strip all scale with amps, not watts. Halving the current by moving to 24 V is the single easiest way to run a longer strip cleanly.

What size power supply should I buy?

Take the total wattage and add headroom so the supply is not pinned at its limit. The common rule is 20%, which the tool applies by default: a 72 W load wants a supply rated at least 72 × 1.2 = 86.4 W, so you would pick the next standard size up, often a 100 W unit. Running a supply at 100% of rating shortens its life and runs it hot, which is why nobody sizes a brick to exactly the load.

12 V versus 24 V — which strip voltage should I choose?

For the same brightness the two draw the same watts, but the 24 V strip pulls half the current, so it suffers half the voltage drop and can run roughly twice as far before the far end dims. A 5 metre run is comfortable at 12 V; past about 5 metres, 24 V is the cleaner choice. 5 V addressable strips are the worst for drop and rarely run past 2 metres without re-injecting power.

My strip is dimmer at the far end — what is going on?

That is voltage drop. Current flowing along the thin copper traces of the strip loses a little voltage every metre, so the LEDs farthest from the supply see less voltage and glow dimmer or shift colour. The fix is to feed power at both ends of the run, split a long run into shorter segments each fed from the supply, or move to 24 V. This tool warns you once a run passes the practical length for its voltage.

Can I run two strips from one power supply?

Yes, as long as the supply rating clears the combined load plus headroom. Add the wattage of both strips first: two 4 metre 9.6 W/m strips draw 2 × (9.6 × 4) = 76.8 W, so with 20% headroom you need a supply rated about 92 W. Wire each strip back to the supply rather than daisy-chaining a long single run, which keeps voltage drop down on both.

Pick the power brick for an under-cabinet kitchen run

You are wiring 4 metres of 14.4 W/m warm-white strip under the upper cabinets at 12 V. Punch in 14.4, 4 m, 12 V and read 57.6 W of load, 4.8 A, and a recommended supply of about 69 W. Buy the next standard size up, usually a 100 W brick, and the run lights to full brightness with the supply loafing well under its limit instead of buzzing hot.

Check whether a supply you already own is big enough

A 60 W 12 V adapter is in the parts bin. Switch to reverse mode, enter 60 W and your strip's 14.4 W/m, and the tool says it tops out around 4.1 metres. If your run is 5 metres you are over budget, so either cut the run, run two adapters, or step to a 24 V strip that draws less current and stretches further on the same wattage.

Decide between 12 V and 24 V for a long cove run

A 9 metre cove of 9.6 W/m strip draws 86.4 W either way, but at 12 V that is 7.2 A and the far end will visibly dim, while 24 V is 3.6 A and stays even. The tool flags the 12 V run as past its practical length and clears the 24 V one, which settles the wire-gauge and voltage-drop argument before you order the reels.

Size a sign or display backlight build

A backlit acrylic sign uses 2.5 metres of 19.2 W/m COB strip at 24 V. That is 48 W and 2 A, calling for a roughly 58 W supply. Copy the one-line result into your build notes or the bill of materials so the supply, fuse and wire are all specced to the same number rather than guessed from the strip box.

LED Strip Power Calculator — Wattage, Current + Power Supply Size

W/m × length = total watts · watts ÷ volts = amps · +20% headroom sizes the supply · 5V / 12V / 24V · browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Size the power supply for an LED strip run. Enter watts per metre, the run length and the strip voltage to read total power, total current and the supply wattage you should buy. Switch to reverse mode to find how much strip a supply you already own can run.

Mode

Common densities

Power per metre (W/m)

Strip length (m)

Supply headroom (%)

Strip voltage

Result

Total power

72 W

Total current

6 A

Recommended supply

86.4 W

P = W/m × length · I = P / V · Supply = P × (1 + margin)

Voltage drop: Single-end feed is fine for a run this short.

What this tool does

Free LED strip power supply calculator for planning under-cabinet, cove, shelf and accent lighting. Tell it the strip rating in watts per metre, how long the run is, and whether it is a 5 V, 12 V or 24 V strip. It returns the total power the run draws, the total current at that voltage, and the supply wattage you should actually buy after a 20% headroom so the power brick is not running flat out. A reverse mode flips the question: you already own a 60 W supply, so how many metres of a given strip can it safely run? The far end of a long low-voltage run dims because of voltage drop, so the tool flags when a run is long enough to need power injected at both ends or a move to 24 V. Everything is plain arithmetic in your browser with one-click copy and a shareable URL that reopens the exact run. 100% client-side, no upload, no account.

Tool details

Input: Files + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How LED Strip Power Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Pick the power brick for an under-cabinet kitchen run
You are wiring 4 metres of 14.4 W/m warm-white strip under the upper cabinets at 12 V. Punch in 14.4, 4 m, 12 V and read 57.6 W of load, 4.8 A, and a recommended supply of about 69 W. Buy the next standard size up, usually a 100 W brick, and the run lights to full brightness with the supply loafing well under its limit instead of buzzing hot.
Check whether a supply you already own is big enough
A 60 W 12 V adapter is in the parts bin. Switch to reverse mode, enter 60 W and your strip's 14.4 W/m, and the tool says it tops out around 4.1 metres. If your run is 5 metres you are over budget, so either cut the run, run two adapters, or step to a 24 V strip that draws less current and stretches further on the same wattage.
Decide between 12 V and 24 V for a long cove run
A 9 metre cove of 9.6 W/m strip draws 86.4 W either way, but at 12 V that is 7.2 A and the far end will visibly dim, while 24 V is 3.6 A and stays even. The tool flags the 12 V run as past its practical length and clears the 24 V one, which settles the wire-gauge and voltage-drop argument before you order the reels.
Size a sign or display backlight build
A backlit acrylic sign uses 2.5 metres of 19.2 W/m COB strip at 24 V. That is 48 W and 2 A, calling for a roughly 58 W supply. Copy the one-line result into your build notes or the bill of materials so the supply, fuse and wire are all specced to the same number rather than guessed from the strip box.

Common pitfalls

Sizing the supply to exactly the load. A 72 W run needs more than a 72 W brick — add headroom, typically 20%, so the supply runs cool and lives long. A brick pinned at 100% gets hot, drops voltage and fails early.
Forgetting that current, not wattage, sets the wire and connector. Two strips at the same wattage pull very different amps at 12 V versus 24 V. Spec the wire gauge and connector rating from the amp figure the tool gives, not from the watts.
Ignoring voltage drop on long runs. A 12 V strip stretched past about 5 metres dims toward the far end no matter how big the supply is. Feed both ends, split the run, or move to 24 V instead of just buying a bigger brick.

Privacy

Every number here — the watts-per-metre multiply, the current divide, the headroom and the reverse length solve — is plain JavaScript that runs in your browser tab. No strip length, voltage or supply size ever leaves the page, and nothing is logged. The one caveat: the shareable URL encodes your inputs in the query string, so a "share link" pasted into chat will record those values in the recipient server's access log. For a private install plan, use the copy button and paste the text rather than the URL.

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LED Strip Power Calculator — Wattage, Current + Power Supply Size

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How LED Strip Power Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Pick the power brick for an under-cabinet kitchen run

Check whether a supply you already own is big enough

Decide between 12 V and 24 V for a long cove run

Size a sign or display backlight build

Common pitfalls

Privacy

FAQ

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