A wire that is too thin is one of the most common reasons an LED strip becomes dimmer toward the end, changes color compared with the beginning, or causes the insulation to become warm. The reason is voltage drop: the wire size is insufficient for the current and line length, so part of the supply voltage is lost before it reaches the strip. The calculator below determines the minimum and recommended wire cross-section for your specific parameters — enter the power (or current), line length, and allowable voltage drop.
Calculator
Wire size for LED strips — 12 V and 24 V
Enter the power (or current), the distance from the power supply to the LED strip, and the allowable voltage drop. The calculator will determine the minimum and recommended wire cross-section.
Recommended wire cross-section
This value is usually printed on the cable packaging or included in the cable specification (for example, 2×0.50 mm²)
Enter the power and line length to calculate the result.
⌀ — mm
conductor, not to scale
How the calculator works
The wire cross-section is selected so that the voltage drop does not exceed the specified percentage of the supply voltage. In 12 V and 24 V systems, even a small voltage drop can noticeably affect brightness and color, so this requirement often determines the required wire size.
L — one-way line length (m), I — current (A), ρ — conductor resistivity (copper 0.0175, aluminum 0.028 Ω·mm²/m), U — supply voltage. The result is rounded up to the next standard wire cross-section.
Reference table for short cable runs
Basic power/current/wire-size relationships without line-length correction. This is useful for short connections close to the power supply. For an accurate result that includes the actual cable length, use the calculator above.
| Power | Current | Diameter | Cross-section |
|---|---|---|---|
| 12 W | 1 A | 0,75 mm | 0,44 mm² |
| 24 W | 2 A | 1,0 mm | 0,79 mm² |
| 48 W | 4 A | 1,5 mm | 1,77 mm² |
| 72 W | 6 A | 2,0 mm | 3,14 mm² |
| 100 W | 9 A | 2,5 mm | 4,91 mm² |
This calculator selects wire size based on voltage drop. Always verify the allowable current for the specific cable, ambient temperature, installation method, and manufacturer requirements. High-power circuits may also require dedicated protection and multiple power injection points.
Why wire size matters so much in 12 V and 24 V systems
In a 220 V mains circuit, losing 2–3 V is less than 1.5% and is usually insignificant. Low-voltage LED systems are very different: the same 2–3 V loss on a 12 V line represents roughly 15–25% of the supply voltage. This is why LED installations are usually designed around an allowable voltage drop of about 2–5% rather than generic household wiring tables.
The effects of undersized wire appear gradually. First, the far end of the LED strip becomes dimmer and the white color may shift, especially on dense or high-current RGB/RGBW strips. With sustained load, the wire and insulation may also heat up, which becomes a safety issue. Excessively oversized wire also increases cost and makes installation more difficult, so the goal is to select a size appropriate for the actual power and cable length.
How the calculator works
The calculation is based on the standard conductor voltage-drop formula:
S = (2 × L × I × ρ) / ΔU, where ΔU = U × (allowable drop% / 100)
L — one-way line length in meters, I — load current in amperes, ρ — conductor resistivity (0.0175 for copper and 0.028 Ω·mm²/m for aluminum), and U — supply voltage. The factor of 2 accounts for current traveling through both conductors, to the strip and back to the power supply. The calculated value is rounded up to the next commonly available wire cross-section (0.5; 0.75; 1; 1.5; 2.5; 4; 6; 10; 16 mm²).
12 V vs 24 V: why 24 V needs much less wire cross-section for the same power
At the same power, a 24 V line carries half the current of a 12 V line (I = P / U). At the same allowable percentage voltage drop, the permitted absolute voltage drop ΔU is also twice as large at 24 V. Both factors reduce the required wire size: theoretically, the required cross-section for the same power, length, and percentage drop is approximately four times smaller. After rounding to standard wire sizes, the practical difference may be smaller.
This is why 24 V systems are especially practical for longer runs and higher-power projects such as perimeter lighting, long architectural lines, retail spaces, and other commercial installations. 12 V remains a convenient option for short, lower-power sections where cable losses are small.
If the calculated wire size becomes impractically large, it is often better to add several power injection points closer to the load rather than continue increasing the cable size. This is usually cheaper and easier to install. A short-run reference table for 12 V and 24 V systems is also available in the article about calculating wire size for LED strips.
Calculation examples
Example 1. An LED strip draws 96 W from a 12 V supply. The one-way cable length is 5 meters, the allowable voltage drop is 3%, and the conductor is copper. Current: I = 96 / 12 = 8 A. Calculated cross-section: S ≈ 3.89 mm² → round up to the standard 4 mm² size. The actual voltage drop is approximately 2.92%, which is within the 3% target.
Example 2. A higher-power 24 V example: 200 W, a 10-meter one-way cable run, 3% allowable voltage drop, and copper conductors. Current: I = 200 / 24 ≈ 8.33 A. Calculated cross-section: S ≈ 4.05 mm² → round up to the standard 6 mm² size. Actual voltage drop is approximately 2.02%. This illustrates the practical advantage of 24 V on longer runs.
Common mistakes when choosing wire for LED strips
- Ignoring the actual cable length. Generic "power → wire size" tables are often intended for very short connections near the power supply and may underestimate the required wire size for longer runs.
- Using aluminum instead of copper. Aluminum has higher resistivity and therefore needs a larger cross-section for the same voltage-drop performance. It also requires suitable terminals and connection practices. Copper is generally the more practical choice for LED projects.
- Using one oversized cable instead of multiple power injection points. It is often easier and cheaper to inject power at several points along the LED strip than to run one very large cable from a single point.
- Correct wire size but undersized connectors or terminals. Correctly sized cable does not help if a connector, plug, or terminal block is rated for less current than the circuit actually carries.
- Ignoring installation conditions. Cable installed in an enclosed conduit or trunking without ventilation can run hotter than the same cable in open air. Installation conditions should be considered when choosing the final cable.
Frequently asked questions
Can aluminum wire be used for LED strips?
Technically yes, and the calculator includes an aluminum option. However, aluminum requires a noticeably larger cross-section for the same current and cable length and requires suitable connection hardware. Copper is generally more practical and reliable for LED projects.
What if the calculator requires more than 16 mm²?
This usually means that one cable run of that length and power is becoming impractical. Consider adding a power injection point closer to the load or using a separate power supply for the remote section instead of continuing to increase the cable size.
12 V or 24 V — which should you choose for a new project?
There is no single answer because the choice depends on total power and cable length. 12 V remains common and convenient for short, lower-power sections. For longer runs or higher total power, 24 V can significantly reduce the required cable size for the same percentage voltage drop.
Do you need to calculate wire size for a short cable run?
For very short connections, voltage drop is often small, but the cable ampacity still has to match the load. The table below the calculator can be used for a quick estimate, while high-power sections should also be checked against the actual cable rating and installation conditions.
If you still have questions about selecting a power supply or cable for a specific project after using the calculator, contact us and we will help you choose.
