LED Strip Power Supply Calculator
How to Use the LED Strip Power Supply Calculator
This calculator helps you choose a safe, reliable power supply for your LED strip lighting. Enter three values: the total strip length, the power consumption in watts per meter, and the strip voltage (usually 12 V or 24 V). The calculator then estimates how many watts and amps your power supply should be able to provide, including a practical safety margin.
Use the tool before you buy an adapter or driver, or when you are checking whether an existing power supply can safely run a new strip. It is designed for constant-voltage LED strip lights commonly sold on reels.
Step-by-step
- Measure strip length: Add up the total length of LED strip that will be powered from one power supply output (for example, 4.5 m for under-cabinet lighting).
- Find watts per meter: Look on the LED strip reel, packaging, or datasheet for a value like
4.8 W/m
,9.6 W/m
, or similar. Enter that number in the calculator. - Confirm strip voltage: Most household LED strips are 12 V or 24 V constant-voltage. Match the calculator’s voltage to the strip rating printed on the strip or its power supply.
- Calculate: Press the button to see the approximate minimum wattage and current rating your power supply should have, plus a recommended overhead margin.
Core Formulas for LED Strip Power
The calculator uses straightforward electrical formulas to estimate your required power supply size. Knowing these makes the results easier to understand and double-check.
- Total power (watts) without margin: strip length × watts per meter.
- Recommended power (watts) with margin: total power ÷ (1 − safety margin).
- Current (amps): power (watts) ÷ strip voltage.
In mathematical notation, the key relationships are:
where P is total strip power in watts, L is strip length in meters, and Pm is power per meter in watts per meter.
The recommended power supply rating with a safety margin factor k (for example 0.2 for 20 %) is:
and the corresponding current draw from a power supply with voltage V is:
Interpreting Your Results
When you use the calculator, you will typically see three useful numbers:
- Total LED load (W): The approximate power the strip itself consumes, without any extra margin.
- Recommended power supply wattage (W): The minimum rating your power supply should have after adding a safety margin. Choose an adapter or driver with at least this rating or the next standard size up.
- Required current (A): The estimated current drawn at the specified voltage. This helps you confirm that both the power supply and the wiring are rated for the load.
For example, if the calculator outputs a recommended supply wattage of 36 W and a current of 3 A at 12 V, any 12 V power supply rated for 36 W or more (3 A or more) is acceptable. Many people will choose a common size such as 12 V 5 A (60 W) to allow room for expansion.
Worked Example: Under-cabinet LED Strip
Imagine you are planning an under-cabinet lighting project in your kitchen. You want a single-color LED strip running along the bottom of your cabinets.
Project details
- Total strip length: 4.5 m
- Strip rating: 4.8 W/m at 12 V (a common density strip)
- Supply voltage: 12 V
- Safety margin: 25 % (typical for comfortable operation)
Step 1 — Calculate LED load
Total LED power without margin:
4.5 m × 4.8 W/m = 21.6 W
Step 2 — Add safety margin
With a 25 % margin, the supply should not be run above 75 % of its rating. So we divide by 0.75:
21.6 W ÷ 0.75 ≈ 28.8 W
Any 12 V power supply of 30 W or more is therefore suitable. Common sizes are 12 V 3 A (36 W) or 12 V 5 A (60 W). The calculator will give you a similar recommended minimum wattage.
Step 3 — Estimate current
Using P = V × I, we solve for I:
I = 28.8 W ÷ 12 V = 2.4 A
This means:
- The power supply must be rated for at least 2.4 A at 12 V.
- Your wiring and connectors should be able to handle at least this current comfortably.
Typical Power Usage for Common LED Strip Types
If you cannot immediately find the wattage per meter for your strip, use these typical ranges as a starting point, then confirm against the manufacturer’s data whenever possible.
| Strip type | Example description | Typical power (W/m) |
|---|---|---|
| 3528, 30 LEDs/m | Basic accent, single color | 2–3 W/m |
| 3528, 60 LEDs/m | Medium brightness, single color | 4–5 W/m |
| 5050, 30 LEDs/m | High brightness, single color | 7–9 W/m |
| 5050, 60 LEDs/m | Very bright, single color | 14–18 W/m |
| RGB 5050, 30 LEDs/m | Color-changing | 7–10 W/m |
| RGB 5050, 60 LEDs/m | Color-changing, high output | 14–20 W/m |
| RGBW / tunable white | Multi-channel white or RGBW | 15–24 W/m (varies widely) |
These numbers are indicative only. Always defer to the specific strip’s datasheet if available, especially for high-density or specialty products.
Example Power Supply Size Guide
After you know your required wattage, you still have to select an actual power supply size. Many manufacturers offer standard wattage ratings. The table below shows illustrative mappings between LED load and a convenient power supply size for a 12 V system.
| Total LED load (W) | Suggested minimum supply (W) | Approx. current at 12 V (A) |
|---|---|---|
| Up to 24 W | 30 W supply | Up to 2.5 A |
| 25–48 W | 60 W supply | 2.1–4.0 A |
| 49–96 W | 100 W supply | 4.1–8.0 A |
| 97–144 W | 150 W supply | 8.1–12.0 A |
| 145–192 W | 200 W supply | 12.1–16.0 A |
For 24 V systems, the wattage recommendations are similar but the current is roughly half for the same power level, which can make wiring easier.
Limitations and Assumptions of This Calculator
To keep the tool simple and broadly useful, several assumptions are made. Be aware of them when interpreting the results.
- Constant-voltage strips only: The calculator assumes LED strips designed for constant-voltage (for example 12 V or 24 V) operation, which is what most flexible LED tape uses. It is not intended for constant-current LED modules or bare LED arrays.
- Uniform power per meter: It assumes the power draw is constant along the entire length of the strip and matches the watts-per-meter value you enter.
- Single feed point: Calculations assume that the specified length is powered from one power supply output, typically from one end of the strip. Very long runs often require power injection at multiple points to avoid visible dimming.
- Safety margin range: The recommended wattage typically includes a margin in the 20–30 % range, which is suitable for many installations. Heavy-duty or commercial applications may require larger margins depending on environment and duty cycle.
- Nominal voltage: The formulas use the strip’s rated voltage (for example 12 V). Real supplies can vary slightly, but this approximation is sufficient for sizing.
- Ambient temperature: Heat affects both LEDs and power supplies. The calculator does not derate for high-temperature environments; if your project will run in a hot area or an enclosed box, consider choosing a larger power supply than the minimum.
Always cross-check results with the manufacturer’s datasheet for your specific strip and power supply if available.
Planning for Longer Runs and Expansion
As LED strip runs become longer, two practical issues become more important: voltage drop and future expansion.
Voltage drop considerations
Low-voltage systems such as 12 V LED strips can lose noticeable voltage along long runs or thin wires. This can cause the far end of the strip to look dim or shift slightly in color.
- Use shorter runs: Split very long lengths into separate runs, each powered directly from the supply or a distribution block.
- Inject power: Feed power to both ends of the strip or at intervals along the run using heavier-gauge cable.
- Consider 24 V strips: For long, continuous lines of light, 24 V strips often suffer less noticeable voltage drop than 12 V equivalents at the same power level.
Allowing for future additions
If you expect to add more LED strip segments later, choose a power supply with extra capacity above the calculator’s minimum. For example, if your current project requires around 40 W, a 60 W or 75 W power supply can leave room for additional short runs or brighter strips in the future.
Safety and Best Practices
Working with low-voltage LED strips is generally safe, but electrical loads still need to be handled correctly. Keep these guidelines in mind:
- Match voltage exactly: Never power a 12 V strip with a 24 V supply or vice versa. Over-voltage can permanently damage the LEDs or create a fire risk.
- Do not overload supplies: Avoid running a power supply at 100 % of its rating for extended periods. The calculator’s margin helps, but if in doubt, size up.
- Check wire ratings: Ensure that any extension wire between the power supply and the strip is rated for the calculated current. Longer runs and higher currents may require thicker wire.
- Ventilation: Mount power supplies in locations with adequate airflow and away from flammable materials. Enclosed or hot spaces often require derating or oversizing the supply.
- Fusing and protection: For larger installations, use appropriate fuses or DC breakers to protect wiring, especially if you are distributing power to multiple runs.
- Local codes and professionals: For extensive or permanent installations, consult local electrical codes or a qualified electrician. This is particularly important when working with mains-voltage input to power supplies.
Summary
The LED Strip Power Supply Calculator turns three simple inputs — strip length, watts per meter, and supply voltage — into clear guidance on the required power supply wattage and current. By understanding the underlying formulas, respecting the built-in assumptions, and applying basic installation best practices, you can design LED strip projects that are bright, efficient, and reliable.