Correctly calculating power requirements prevents underpowered systems (dim LEDs, flickering) and overpowered systems (wasted money, oversized equipment). This guide gives you the formulas and practical examples.
The Basic Formula
Total Power (W) = Watts per meter × Total length (meters)
Every LED strip product specifies its wattage per meter. Common values:
- Low density (30 LEDs/m): 4-8W/m
- Medium density (60 LEDs/m): 8-14W/m
- High density (120 LEDs/m): 14-24W/m
- Ultra-high density (240 LEDs/m): 20-30W/m
Adding the Safety Margin
Always multiply your calculated total by 1.2 (20% margin):
PSU Rating = Total Power × 1.2
This margin accounts for power supply aging, temperature derating, and unexpected additions to the installation.
Example Calculation
Project: 15 meters of 60 LEDs/m RGB strip rated at 14.4W/m
- Total power: 14.4W/m × 15m = 216W
- With margin: 216W × 1.2 = 259.2W
- Choose a 300W power supply (next standard size above 259.2W)
Voltage Drop Considerations
Voltage drop becomes significant on longer runs. As a rule of thumb:
- 12V strips: Inject power every 5 meters
- 24V strips: Inject power every 10 meters
If you cannot add injection points, calculate the voltage drop:
Voltage Drop (V) = Current (A) × Wire Resistance (Ω)
If the drop exceeds 10% of your supply voltage, you need thicker wire or additional injection points.
Multiple Power Supplies
For large projects, it’s often better to use multiple smaller power supplies rather than one large unit:
- Easier to distribute around the installation
- Redundancy — if one fails, only part of the system goes dark
- Easier to replace and maintain
Wire Sizing Guide
| Run Length | Current | Recommended Wire |
|---|---|---|
| 0-3m | Up to 5A | 22 AWG |
| 3-5m | Up to 10A | 20 AWG |
| 5-10m | Up to 15A | 18 AWG |
| 10m+ | 15A+ | 16 AWG |
Quick Reference Table
| Strip Length | 8W/m Strip | 14.4W/m Strip | 24W/m Strip |
|---|---|---|---|
| 5m | 48W → 60W PSU | 86W → 100W PSU | 144W → 175W PSU |
| 10m | 96W → 120W PSU | 173W → 200W PSU | 288W → 350W PSU |
| 15m | 144W → 175W PSU | 259W → 300W PSU | 432W → 2×300W PSU |
| 20m | 192W → 250W PSU | 346W → 400W PSU | 576W → 2×350W PSU |
PSU values include 20% safety margin, rounded to nearest standard size.