Ask a GPU host what a rental hour earns and you get an exact number. Ask what that hour costs in electricity and you usually get a shrug. Power is the one recurring cost in this business, and guessing at it means every margin figure you compute downstream is fiction. The Power Cost Calculator replaces the guess with a per-machine number: dollars per hour, per day, per month.
Why hosts get their power cost wrong
The naive estimate is GPU TDP times electricity rate, and it is wrong in a predictable direction: too low. A rig draws power beyond its GPUs. The CPU, motherboard, RAM, drives, and fans all pull watts, the power supply loses a percentage to conversion, and a server chassis has different overhead than a desktop tower. Hosts who run their mental math at GPU-only wattage systematically overestimate their margin, and some discover their cheapest rentals were actually losing money.
Getting this number right matters because it anchors everything else: your price floor, your weekend override floors, and the decision of whether a card is worth listing at all.
What the calculator takes in, and what it gives back
Three inputs, one honest answer:
- Your electricity rate in $/kWh. Pull it from your utility bill, and use the all-in rate including delivery charges, not just the generation line item.
- Your system type. Desktop, server, and other chassis types carry different overhead multipliers, so the calculator accounts for the power your non-GPU components draw instead of pretending the GPUs run in a vacuum.
- TDP per GPU. Pre-filled presets cover common models, and you can adjust the value if you run custom power limits.
Out comes the electricity cost of running that machine: hourly, daily, and monthly. The hourly figure is the one that plugs directly into pricing decisions, because rentals are billed by the hour.
Worked example: a 2x RTX 4090 desktop
Take a desktop rig with two RTX 4090s at their stock 450 W TDP and an all-in electricity rate of $0.14/kWh.
- 1GPU draw at full load: 2 times 450 W is 900 W.
- 2Apply the desktop overhead multiplier for CPU, board, drives, fans, and PSU losses. Call the resulting system draw roughly 1,080 W, or 1.08 kW.
- 3Hourly cost: 1.08 kW times $0.14 is about $0.15 per hour, which is $0.075 per GPU hour.
- 4Daily and monthly at full load: about $3.63 per day and $109 per month.
Now the number starts working. If comparable 4090s are clearing at $0.35 per GPU hour, your gross margin over power is about $0.275 per GPU hour, or roughly 79%. If a weekend market dip tempts you toward $0.10, you now know that keeps only $0.025 per GPU hour over electricity, and you can decide with open eyes instead of round numbers.
Idle machines still draw power
From power cost to price floor
The per-GPU-hour power cost is the hard bottom of your pricing. Below it, every rented hour loses money; above it, the question is how much margin you want against how much idle time you can tolerate. A common structure: set your price floor at power cost plus your target margin, and treat the gap between power cost and floor as your negotiating room for scheduled weekend overrides. The full break-even method, including hardware payback, is in the guide on setting your price floor.
Shrinking the cost side: power limits
The calculator also makes the case for power limiting, because it quantifies the savings. RTX 4090s lose very little rentable performance at reduced power targets, and the wattage delta drops straight to your margin:
| Setting | System draw | Cost per GPU hour | Monthly cost |
|---|---|---|---|
| 2x 4090 at 450 W | ~1.08 kW | ~$0.075 | ~$109 |
| 2x 4090 at 360 W | ~0.88 kW | ~$0.062 | ~$89 |
That is roughly $20 a month back on one machine at $0.14/kWh, more in expensive markets, for a performance cost most renters never notice. Rerun the calculator with the new TDP values to see your own numbers. The how and the trade-offs are covered in the GPU power limit guide, and the command-line specifics live in our open source nvidia power limit reference.
Make it a habit, not a one-off
Electricity rates change, hardware gets added, and power limits get tuned, so revisit the calculator whenever any input moves. The rhythm that works: recalculate on every rate change or hardware change, then sanity-check your floors against the new cost. Your cost basis is the one part of this business the market cannot move, which makes it the most reliable foundation to price from. When your floor is grounded in a real number, the next step is choosing how aggressively to compete above it, and that is a pricing strategy question.