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A NAS running 24/7 uses about 8.76 kWh per year for every watt of average power. Multiply that annual energy by your electricity price per kWh to estimate its electricity cost. For example, a NAS averaging 32.41 W would use about 284 kWh a year—roughly $49 a year, or $4.09 a month, at the U.S. 2025 average residential rate of 17.30¢/kWh. That is an illustration, not a universal bill: your NAS’s workload, installed drives, hours of operation, and local tariff determine your actual cost.
Calculate the electricity cost of a 24/7 NAS
The calculation uses average power, not the maximum wattage printed on a power supply. Power is measured in watts (W); energy used over time is measured in kilowatt-hours (kWh), which is what electricity bills charge for. A watt is a rate of using energy at a moment in time. A kilowatt-hour accumulates that use over time: a steady 1,000 W load running for one hour consumes 1 kWh.
- Find average power in watts. Use a whole-system wall measurement over representative days or weeks if possible. Include the NAS and installed drives.
- Calculate annual energy. For continuous operation, multiply average watts by 8.76. This factor comes from 8,760 hours in a 365-day year divided by 1,000 watts per kilowatt.
- Multiply annual energy by your electricity price. Use the applicable price per kWh from your bill, including relevant delivery charges where applicable.
- Divide the annual cost by 12 to get a monthly average. Your bill will not necessarily show that exact amount each month if your tariff, usage, or operating schedule changes.
Formula: Annual kWh = average watts × 8.76. Annual electricity cost = annual kWh × price per kWh. Monthly average = annual cost ÷ 12.
A quick mental check: a continuous 1 W load uses 8.76 kWh per year. A 10 W average load therefore uses 87.6 kWh per year before applying the electricity price. At 17.30¢/kWh, those loads would cost about $1.52 and $15.15 per year, respectively. Small differences in watts can add up over a full year, but the price depends on the rate you actually pay.
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What the calculation looks like with a real NAS specification
Synology lists 32.41 W in “Access” and 4.97 W in “HDD Hibernation” for its four-bay DiskStation DS423. These are manufacturer-published readings for distinct test states, not measurements of a household’s year-long average. The following calculations show what each reading would cost if it were sustained continuously.
| DS423 test state | Published power | Annual energy if sustained 24/7 | Annual cost at 17.30¢/kWh | Monthly average at 17.30¢/kWh |
|---|---|---|---|---|
| Access | 32.41 W | About 284 kWh | About $49 | About $4.09 |
| HDD Hibernation | 4.97 W | About 43.5 kWh | About $7.53 | About $0.63 |
The 17.30¢/kWh rate is the U.S. average residential electricity price reported by the U.S. Energy Information Administration for 2025. It is a national comparison point, not a rate for every household. At the EIA’s 18.21¢/kWh estimate for 2026, the same continuously sustained 32.41 W example works out to about $52 a year. That 2026 figure is an outlook estimate, not a final observed annual average; local rates vary.
The table is useful for understanding scale, not for predicting the exact charge on a DS423 owner’s bill. The Access row assumes that its published Access-state reading lasts every hour of the year; the HDD Hibernation row makes the same assumption about the separate low-power test state. Neither row describes a typical mix of activity. The correct number for a particular home depends on the average wall power over its own operating pattern and configuration.
Why the NAS’s actual average may differ
It spends time in more than one power state
A NAS may draw different amounts of power while serving files, running background work, or with its hard drives in a low-power state. Synology describes its HDD-hibernation measurement as measuring the device when all HDDs are in low-power mode. That definition matters: the hibernation figure is not a promise that a NAS will remain at that power level during ordinary use, or that every model will hibernate in the same way.
If you know how much time your NAS spends in each state, estimate a weighted average instead of treating one reading as the all-day value. Multiply the watts for each state by the share of time spent there, then add the results. For example, if the DS423 spent exactly half its time at its published 32.41 W Access reading and half at its published 4.97 W HDD Hibernation reading, the weighted average would be 18.69 W. At that assumed schedule, it would use about 164 kWh a year and cost about $28.32 a year, or $2.36 a month, at the 2025 U.S. average rate. This is a mathematical illustration, not a claim about a typical household’s usage or the DS423’s observed behavior.
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For a more detailed schedule, calculate each state separately: watts × hours in that state ÷ 1,000 gives kWh for that period. Add the state totals for the day, week, or year, then multiply the resulting kWh by the relevant price. If access, backups, and low-power periods vary from day to day, a wall measurement across representative days or weeks can capture that mix more practically than estimating every state individually.
Background indexing, media serving, backups, containers, and frequent file access can affect whether the drives reach a low-power state. Their effect depends on the workload and configuration; the published state readings do not quantify a universal increase or decrease for those activities. Hibernation can reduce energy use when it occurs, but it is not automatically the right goal: availability and workload needs matter, and a NAS that must serve files or perform tasks cannot always be treated as idle.
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Drives and configuration affect the whole system
A model specification describes a defined test configuration. Your installed drive count and type, and any attached devices drawing power from the same setup, can change the wall measurement. Do not assume a published number applies exactly to a unit with a different configuration. For a useful comparison between two setups, measure both as complete systems under the same representative workload, with their installed drives and comparable operating schedules.
This is one reason a specification is best treated as a reference point rather than a guaranteed household value. When comparing models, note whether the readings describe the same kind of operating state and whether the systems have comparable drives installed. An enclosure-only number and a whole-system measurement are not necessarily measuring the same thing.
Hours powered change annual energy
The 8.76 multiplier assumes the device runs all 8,760 hours of a 365-day year. If you shut it down on a schedule, calculate energy using the actual operating hours instead: average watts × hours powered ÷ 1,000 = kWh. For several different states, calculate each state’s energy from its watts and hours, then add the results. Scheduled downtime reduces electricity use but also makes the NAS unavailable during those hours, which may matter for backups, remote access, or other services.
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There is no need to assume a device runs continuously just because it is called a 24/7 NAS. Conversely, if it is powered on all year, using a few hours of downtime in the calculation would understate its energy use. Make the run-time assumption explicit so someone can reproduce or adjust the estimate.
Your tariff matters as much as the wattage
The U.S. national average is useful for context, but it cannot replace your local electricity price. Look at the rate that applies to the additional consumption on your account; where relevant, include delivery charges. If your bill uses different rates at different times, apply the appropriate rate to the energy used in each period rather than treating a national average as your personal cost.
The EIA’s 2025 figure of 17.30¢/kWh is an annual U.S. residential average, while its 18.21¢/kWh figure for 2026 is an outlook estimate. These are useful reference prices for illustrating the calculation, not a substitute for checking your own bill. Geography and tariff structure can change the dollar result even when two households use identical NAS hardware.
How to get a more reliable estimate for your setup
- Choose a representative period. A measurement over several typical days or weeks is more useful than a single moment, especially if your NAS alternates between active and quiet periods. Include normal backups, file access, and other routine work.
- Measure at the wall. Use a suitable whole-system wall measurement so the reading includes the NAS and its installed drives. A power-supply rating is not a substitute: it describes the supply’s capacity, not how much electricity the NAS actually draws in your home.
- Record the operating context. Note the drive configuration, whether the NAS is serving files or doing background work, and any periods when it is off or in a low-power state. These details help explain why your reading differs from a vendor’s published test figure.
- Use the measured average in the formula. Multiply average watts by 8.76 for a 24/7 annual estimate, then multiply by your applicable price per kWh. If the device has a planned duty cycle, use actual hours or calculate each operating state separately.
- Keep the estimate in scope. Label the result as electricity cost. Purchase price, replacement drives, networking equipment, cooling, and the value of keeping data available are separate costs and are not included in this calculation.
When using a wall meter, take readings during ordinary operation rather than relying on a single idle snapshot. A brief reading may miss a backup or other recurring task, while an unusually busy period may not represent the rest of the week. Record enough context to understand what the average includes, and repeat the estimate if your workload or configuration changes substantially.
How to use the estimate when comparing NAS options
Compare complete setups, not just model names or power-supply labels. For each one, use the same representative workload and measurement approach, then account for its drive configuration, hours powered, and your tariff. Converting both measured averages to annual kWh and cost makes the electricity difference easier to judge.
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Keep electricity separate from other reasons to choose a configuration. Capacity, drive replacement, noise, backup behavior, and availability are not captured by a wattage-to-cost calculation. A lower electricity estimate alone does not show whether the setup meets your storage or uptime needs.
For a fair comparison, keep the assumptions aligned: use the same local electricity rate, the same yearly operating schedule, and a comparable workload. If one setup has more drives or is measured during a different mix of access and idle time, the two figures may reflect those differences as much as the enclosure itself. The useful comparison is the annual electricity cost of each complete setup under the way you expect to use it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What this estimate does—and does not—tell you
This method answers a narrow but useful question: how much electricity the NAS consumes over time and what that energy costs at a specified rate. It does not predict the exact charge on a future bill, because actual power use and the applicable tariff can vary. It also does not turn a manufacturer’s test-state specification into an independent measurement of a configured home system.
For a first-pass estimate, use a model’s published power reading and clearly state the assumed state, hours, and electricity price. For a household estimate, replace the specification with a representative whole-system wall average and replace the national rate with the rate relevant to your bill. Keeping those assumptions visible makes the result reproducible and prevents a low-power test state from being mistaken for a guaranteed 24/7 consumption level.
The scope here is electricity used by the NAS system being measured. It is not a total cost-of-ownership figure: purchase price, replacement drives, networking equipment, and cooling are separate considerations. Nor does the estimate assign a dollar value to having data available whenever needed. Those costs and tradeoffs can matter to a buying decision, but they should not be folded into an electricity-only calculation without stating a broader scope.
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Frequently Asked Questions
How much does it cost to run a NAS 24/7?
There is no single amount that applies to every NAS. Multiply average watts by 8.76 to estimate annual kWh, then multiply by your electricity price per kWh. For example, a continuous 32.41 W load uses about 284 kWh per year and costs about $49 per year at the EIA’s 2025 U.S. average residential rate of 17.30¢/kWh. Your actual cost depends on measured average power and local tariff.
Can I use the wattage printed on the NAS power supply?
No. The power-supply wattage is its capacity rating, not a measurement of what the NAS draws in your home. For a household estimate, measure the complete system at the wall—including installed drives—over representative days or weeks.
Does HDD hibernation mean my NAS will use that little power all the time?
No. Synology’s DS423 specification lists 4.97 W for its HDD Hibernation test state and 32.41 W for Access. Hibernation is a distinct state, defined in Synology’s testing description as all HDDs being in low-power mode. Your NAS’s actual time in each state depends on its workload and configuration.
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Use actual operating hours: average watts × hours powered ÷ 1,000 gives kWh for that period. For a schedule with multiple power states, calculate the kWh in each state separately and add the results. Remember that scheduled downtime also makes the NAS unavailable during those hours.
Does the estimate include the whole cost of owning a NAS?
No. It estimates electricity only. Purchase price, replacement drives, networking gear, cooling, and the value of keeping data available are separate costs and are not included.
The Bottom Line
Bottom line: Estimate a 24/7 NAS’s annual electricity cost with average watts × 8.76 × your price per kWh. Use a representative whole-system wall measurement when possible, since manufacturer test states and PSU ratings are not the same as your home’s year-long average. Keep the assumptions—workload, drives, hours, and local tariff—visible, and treat purchase and replacement costs separately.
Quick Recap
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