The number stamped on your power supply (e.g. "750W") is the maximum it can deliver, not what your computer pulls from the wall. Most home mining PCs draw far less than the PSU rating, and the only way to know for certain is to measure. A plug-in energy meter like a Kill A Watt P3 (around $25 in the US) or any cheap European equivalent will tell you the truth in about ninety seconds.
How to take a reading
- Plug the meter into the wall outlet.
- Plug your PC's power cable into the meter.
- Boot the PC and let it sit idle for a few minutes. Note the watts.
- Start your Malairte miner and let it run for at least 10 minutes so temperatures and clocks stabilise.
- Note the watts again. That is your real load.
What numbers to expect
A modern desktop with no dedicated GPU and a six-core CPU mining flat out usually lands somewhere between 90 and 180 watts. Add a single mid-range GPU and you are looking at 250-450 watts. A two-GPU rig pushing both cards hard can sit at 600-900 watts. Laptops are dramatically lower, often 35-90 watts even with the CPU pinned.
Why this matters
Every electricity calculation downstream depends on this number. If you guess "my PSU is 750W so I must use 750W," you will overestimate your monthly bill by two or three times. Conversely, an old system with a leaky PSU might use more than you think. Measuring once removes the guesswork for the life of the rig.
Bonus: idle vs. load
Compare the idle and load readings. The difference is the actual cost of mining, separate from the cost of just leaving the PC on. Many home miners are surprised to find their idle draw is already 60-100W; the marginal cost of pointing that machine at Malairte for a few hours is much smaller than it looks.