How to find the numbers
The header rating is in your motherboard manual, usually in the fan header section. Most fan headers are rated for 1 A (12 W), and some for 2 A (24 W), as NZXT explains.
The fan's current is on its spec sheet or its sticker, listed as "max current" or "input current". Use the maximum, not the typical figure. For example, Noctua lists the NF-A12x25 at 0.14 A max.
RGB fans: count the fan, not the lights
On most RGB fans, the lights run from a separate cable and header. Phanteks lists the D30-120 at 0.15 A for the fan and up to 0.45 A for its LEDs. Only the fan's figure counts against the fan header.
What if you're over the limit?
- Split the fans across two headers instead of one.
- Use a powered fan hub. It draws power straight from the power supply and only takes the speed signal from the header.
- Keep some spare room. A fan draws more as it starts up, so we suggest staying under about 80% of the rating.
Planning a new layout? Our case cheat sheets show how many fans each spot in popular cases takes.