Power is the bill that shows up whether your rig makes anything or not. The heat, the wear, the noise, all of it is downstream of watts pulled from the wall. Before you plug in a single card, you should be able to do this math in your head, because the wall meter does not care about your optimism.

Start at the wall, not at the spec sheet. A card rated for 320W does not pull 320W total for the system. The rest of the rig pulls power too: the motherboard, the CPU, the RAM, the fans, and the power supply itself wastes a slice as heat. A rig of six 320W cards is not 1,920W. Measure it with a plug-in power meter and you will usually see 2,100 to 2,300W at the wall once you count everything and the PSU’s efficiency loss. That gap is real money, and it only shows up if you measure.

Now turn watts into a bill. The unit you pay for is the kilowatt-hour, which is 1,000 watts running for 1 hour. A rig pulling 2,200W at the wall uses 2.2 kWh every hour. Run it 24 hours and that is 52.8 kWh a day. Over a 30 day month that is 1,584 kWh.

Then multiply by your actual rate. Look at your power bill and find the number in dollars per kWh, and use the real one, including delivery charges and taxes, not the headline supply rate. Rates swing hard by region. Some places sit near $0.10 per kWh. Plenty of places are $0.30 or higher, and parts of Europe have seen $0.40 and up.

Run the same rig at three rates and the picture changes completely:

  • At $0.10/kWh: 1,584 kWh times $0.10 is about $158 a month.
  • At $0.20/kWh: about $317 a month.
  • At $0.35/kWh: about $554 a month.

Same hardware, same heat, same wear. The only thing that changed is the rate, and it nearly quadrupled the cost. This is why two people running identical rigs can have wildly different outcomes, and it has nothing to do with the hardware.

What “pays for itself” means in power terms

Set coin prices aside. In pure energy terms, a rig pays off when what it produces is worth more than the power it burns to produce it. If your rig eats $317 of electricity a month, everything it earns below $317 is you paying to heat a room. The rig is running at a loss the moment the value of its output drops under its power cost, and it will happily keep running at that loss all night because it has no idea.

This is where undervolting earns its keep. Trimming each card from 320W to 230W on a six-card rig cuts wall draw by roughly 540W, which is about 388 kWh a month. At $0.20/kWh that is $78 a month back in your pocket, for output that barely moves. Power is the lever you actually control.

Two costs people forget

First, time-of-use pricing. Many utilities charge more during peak afternoon and evening hours and less overnight. If your rate doubles from 2pm to 8pm, a rig that runs flat out around the clock is paying the premium for 6 hours a day. On a time-of-use plan you may come out ahead running hard overnight and backing off during peak. Read your rate plan and find out if you have peak hours at all.

Second, the cooling tax. Every watt your rig burns becomes heat in the room, and in summer you may be paying a second time to air-condition that heat back out. A rig throwing off 2,200W of heat into a small room in July can add meaningfully to your cooling bill, so the true cost of running it is the power plus the cooling to survive it. In winter that heat offsets your heating, which is a genuine rebate for a few months a year.

One more thing worth checking before you commit: the circuit itself. A standard 15-amp household circuit at 120V tops out near 1,800W of continuous safe load, and code says stay under 80 percent of the breaker rating on a continuous draw. A 2,200W rig will trip that breaker or, worse, cook the wiring in the wall if the breaker is tired. Spread big rigs across separate circuits, or run a dedicated 20-amp line. The power math protects your wallet and your wiring both, and an overloaded circuit is how a mining setup becomes a house fire.

Do the arithmetic before the rig is on the floor. Wall watts times 24, times 30, times your real rate. If that number scares you, it is better to be scared now than on the first bill.