How to use the calculator
- Find the power per metre (or per foot) and the DC voltage on your strip’s datasheet or reel label.
- Enter the total strip length you will install and your desired headroom margin (20% is recommended).
- Enter the one-way wire distance from the power supply or smart controller to the strip feed point.
- Optionally enter the manufacturer’s maximum run length per feed to calculate necessary power injection points.
- Click Calculate to inspect required power supply wattage, current draw, recommended wire gauge (AWG), and a full anti-voltage-drop table.
Formula and electrical principles
P = power per length × length | I = P ÷ V | supply rating = P × (1 + headroom ÷ 100)
Feed points = total length ÷ maximum run length, rounded up. These are the fundamental relations between electrical power, voltage, and current (P = V × I).
R_loop = 2 × distance × R_conductor | V_drop = I × R_loop | % V_drop = (V_drop ÷ V) × 100
Because direct current (DC) requires a complete circuit (positive and negative conductors), the total wire length in the resistance equation is twice the one-way distance (2 × distance). Power lost as heat in the wiring follows Joule’s law: P_loss = I² × R_loop.
Why headroom matters (The 80% Rule)
Running an LED power supply continuously at 100% of its rated capacity generates excess heat, degrades electrolytic capacitors, and shortens driver lifespan. Industry best practice recommends sizing power supplies with at least 20% headroom (operating at no more than 80% continuous load). Many commercial power supplies also require derating when installed in enclosed ceilings, warm utility closets, or environments above 40°C (104°F). Always consult the driver manufacturer datasheet for thermal derating curves.
Units
Power in watts (W), voltage in volts (V DC), current in amperes (A), length and wire distance in metres (m) or feet (ft), conductor cross-sectional area in American Wire Gauge (AWG) and square millimetres (mm²), electrical resistance in ohms (Ω).
Voltage drop & wire gauge selection (Chống sụt áp)
Copper wire possesses internal resistance. When high DC current flows through small-gauge wires, a portion of the voltage is dropped across the wire before reaching the LED strip. For smart addressable strips (such as WS2812B, SK6812, or RGBCCT strips), excessive voltage drop causes noticeable end dimming, flickering, color shifting (especially on pure white), and micro-controller reboots.
The 24V vs 12V Advantage: Because power is voltage multiplied by current (P = V × I), a 24V system draws exactly half the amperage of a 12V system for identical lighting wattage. Because voltage drop is proportional to current, and that drop is evaluated against a 24V baseline, a 24V system reduces percentage voltage drop by 75% compared to 12V over the same wire gauge and distance. For runs longer than 5 metres (16 ft), 24V strips are strongly recommended.
Standard copper wire gauges (AWG) & DC resistance benchmarks
| Wire Gauge (AWG) | Metric Area (mm²) | Resistance (Ω/m) | Resistance (Ω/1000 ft) | Typical Max Amperage | Recommended LED Applications |
|---|---|---|---|---|---|
| 22 AWG | 0.33 mm² | 0.0530 Ω/m | 16.14 Ω | ~3 A | Short sensor leads, low-power accent strips (< 1.5A, < 2m) |
| 20 AWG | 0.52 mm² | 0.0333 Ω/m | 10.15 Ω | ~5 A | Factory pigtail connectors, short 24V strip runs (< 3m) |
| 18 AWG | 0.82 mm² | 0.0210 Ω/m | 6.385 Ω | ~7 A | Most common residential LED extension wire; under-cabinet task lighting |
| 16 AWG | 1.31 mm² | 0.0132 Ω/m | 4.016 Ω | ~10 A | Heavy-duty 12V/24V runs (3–8m), high-density COB & smart RGBW strips |
| 14 AWG | 2.08 mm² | 0.0083 Ω/m | 2.525 Ω | ~15 A | Long trunk lines (5–15m), main power feed distribution for room perimeters |
| 12 AWG | 3.31 mm² | 0.0052 Ω/m | 1.588 Ω | ~20 A | Centralized driver locations with long home runs (> 15m) |
| 10 AWG | 5.26 mm² | 0.0033 Ω/m | 0.999 Ω | ~30 A | Heavy DC distribution bus for large architectural installations |
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Sources and wire resistance standards
Wire electrical resistance and copper conductor properties are based on standard National Electrical Code engineering tables: NFPA 70 National Electrical Code (NEC) Chapter 9, Table 8: Conductor Properties for copper wire; IEC 60228 (checked 15 October 2026). Calculations use Ohm’s law (V = I × R) and Joule’s law (P = I² × R) for a two-conductor DC loop.
Limits and safety
- This calculator covers the low-voltage DC side only. Connecting a power supply to mains electricity is work for a qualified electrician and must follow the wiring rules where you live. Nothing on this page is wiring instructions.
- Long strips lose voltage along their length, which can make the far end dimmer. The maximum run length from the strip’s datasheet is the reference; use this calculator’s wire sizing and power injection guidance to keep voltage drop below 3% to 5%.
- RGB, RGBW and tunable-white strips may list power at full output of all channels. Use the figure from the datasheet for the highest setting you will use.
- Controllers, dimmers and amplifiers have their own current limits. Check those separately.
Frequently asked questions
How do I calculate the power supply wattage for an LED strip?
Multiply the strip’s rated power per unit length (Watts per metre or foot from the datasheet) by the total installed length to get total strip wattage. Then, add a safety headroom margin of at least 20% (the 80% rule) by multiplying total wattage by 1.20. For example, a 5-metre strip drawing 14.4 W/m requires 72 W of power. With 20% headroom, you need a power supply rated for at least 86.4 W (such as a standard 100 W power supply).
What causes voltage drop in LED strips and how do I prevent it?
Voltage drop occurs because lead wires and thin strip PCB copper traces have internal electrical resistance. As DC current flows through this resistance, voltage decreases along the run according to Ohm’s Law (V = I × R). When voltage drops by more than 3% to 5%, the LEDs at the far end become visibly dimmer, smart controllers can malfunction, and RGB strips show color shifting. Prevent voltage drop by selecting a thicker wire gauge (smaller AWG number), choosing 24V instead of 12V, keeping lead runs short, and injecting power at multiple points.
Which wire gauge (AWG) should I use between the power supply and LED strip?
The recommended wire gauge depends on the total current (Amperes) and the wire distance between the power supply and the strip feed point. For short runs (under 2 metres) with moderate currents (< 3A), 18 AWG or 20 AWG is typically sufficient. For longer runs (3 to 10 metres) or higher currents (5A to 10A on 12V systems), 16 AWG or 14 AWG copper wire is required to keep voltage drop below 3%. Use this calculator’s wire comparison table to inspect the exact voltage drop for your installation.
Why is 24V preferred over 12V for longer smart LED strip runs?
For the same total wattage, a 24V LED strip draws exactly half the current of a 12V strip (P = V × I). Because voltage drop is directly proportional to current (V_drop = I × R), halving the current halves the absolute voltage drop. Furthermore, because that drop is evaluated against a 24V baseline rather than 12V, the percentage voltage drop is reduced by 75% for the exact same wire. This allows 24V strips to run twice as far from a single feed point without dimming.
What is power injection and when is it necessary for LED strips?
Power injection is the practice of running parallel DC power feed wires from the power supply directly to additional points along the strip (such as both ends, or every 5 to 10 metres) rather than powering the entire strip from one end only. It is necessary whenever total strip length exceeds the manufacturer’s maximum single-run limit (typically 5 metres for 12V strips or 10 metres for 24V strips). Power injection ensures that thin internal strip PCB traces do not overheat or carry excessive current.
Can I use a smart dimmer or controller with my LED power supply?
Yes, but the dimmer or smart controller must match your system topology. For low-voltage DC smart lighting (such as Zigbee, Wi-Fi, or RF controllers), you connect a standard non-dimmable constant-voltage power supply to the AC mains, and wire the smart controller on the low-voltage DC side between the power supply and the strip. If you are using an in-wall AC phase-cut (TRIAC/ELV) wall dimmer, you must use a dimmable LED driver specifically rated for phase dimming.