Cost Per Tb Calculator
Two drives can carry similar price tags and wildly different value, because the sticker price says nothing until you divide it by capacity. This cost per TB calculator does that division for a single drive, then goes further: a true yearly cost mode that folds electricity into a head-to-head comparison of two drives.
Use the simple mode when you are scanning listings. Use the true yearly cost mode when a drive will spin around the clock in a NAS or server, where five years of power draw can quietly outweigh a small sticker saving.
A low $/TB is not a buy recommendation. Prices move constantly, and this tool is an estimate aid, not financial advice.
Quick Answer
Key takeaways
- Cost per TB is one division: price divided by advertised terabytes. It is the only fair first comparison between drives of different sizes.
- A drive that runs 24/7 adds an electricity line to its real price. At 6 watts and $0.17 per kWh, that line is $8.94 per drive per year, every year it stays in service.
- Bigger drives usually win on $/TB because the fixed costs of the enclosure, controller, and motor are spread over more terabytes.
- Use the advertised decimal terabytes from the box, not the smaller figure Windows reports. The gap is a units difference, not missing space.
- Quick Answer
- How to use the two modes
- The formulas behind both answers
- Worked example: a sticker tie that is not a tie
- Why Windows shows less space than the box promises
- What a low cost per TB does not tell you
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to use the two modes
Simple mode takes two entries and answers one question: what does each terabyte cost? Enter the full price and the advertised capacity, press Calculate, and the cost per terabyte appears. It accepts prices typed with commas, so 1,200 for an 8 TB drive correctly returns $150.00 per TB.
True yearly cost mode is for a shortlist of two. Enter price, capacity, expected lifespan, and average power draw for each drive, plus your electricity rate, and press Compare true cost. The tool prices a full year of ownership for each drive: one year of the purchase price (price divided by lifespan) plus one year of electricity (watts times 24 hours times 365 days, divided by 1,000 to get kilowatt-hours, times your rate). It then divides by capacity and names the cheaper drive per TB per year. If you are unsure what your electricity rate does to a single device, the cost per kWh calculator breaks a bill down to the per-unit rate this mode asks for.
The formulas behind both answers
Simple mode is a single division. True yearly cost mode adds an energy term and a time term, and every figure it prints can be rebuilt by hand from the four inputs per drive.
Energy per year: watts x 24 x 365 / 1,000 x electricity rate ($/kWh).
Yearly cost: price / lifespan in years + energy per year.
True cost per TB per year: yearly cost / capacity in TB.
The 24/7 assumption is deliberate. A NAS, a home server, or a drive in a recorder never sleeps, so its spec-sheet average wattage runs all 8,760 hours of the year. For a portable drive you plug in twice a week, electricity is a rounding error and simple mode is the honest comparison. The tool does not model cooling, and in a home setting the extra heat from one or two drives is too small to price sensibly. Data centers handle that with a PUE multiplier; a two-bay NAS on a shelf does not need one.
Worked example: a sticker tie that is not a tie
The calculator is pre-filled with this comparison, and every number below is what it returns.
| Figure | Drive A: $179.99, 8 TB | Drive B: $89.99, 4 TB |
|---|---|---|
| Sticker cost per TB | $22.50 | $22.50 |
| Electricity per year (6 W, $0.17/kWh) | $8.94 | $8.94 |
| Yearly cost (price / 5 years + electricity) | $44.93 | $26.93 |
| True cost per TB per year | $5.62 Winner | $6.73 |
Read the table from the top. On sticker price the drives are dead level, which is exactly the result that makes shoppers stop thinking. The yearly view separates them: drive B costs less per year in total, but each of its terabytes carries a full share of the same $8.94 electricity bill, so its cost per TB per year lands $1.12 higher. Over a five-year life in a NAS that always runs, drive A is the cheaper storage even though the two listings looked identical on the only number most tools show. Bars make the shape of the result obvious:
Why Windows shows less space than the box promises
Nothing is missing. Drive makers sell decimal terabytes, where 1 TB is exactly 1,000,000,000,000 bytes, while Windows measures in binary units and labels the result TB. The binary unit has its own name, the tebibyte (TiB), equal to 1,099,511,627,776 bytes, and the binary prefixes behind it are set out in the NIST guide to binary prefixes. Seagate states the industry side plainly in its storage capacity measurement standards: all major drive makers use decimal values for capacity.
| Advertised capacity | What Windows reports | Apparent gap |
|---|---|---|
| 1 TB | 0.91 TiB | About 9% |
| 4 TB | 3.64 TiB | About 9% |
| 8 TB | 7.28 TiB | About 9% |
| 16 TB | 14.55 TiB | About 9% |
For this calculator, always enter the advertised decimal terabytes. That is the capacity you paid for, it is how every listing is priced, and mixing the Windows figure into one drive’s math and the box figure into another’s would corrupt the comparison. macOS reports decimal units, which is why the same drive shows its full advertised size on a Mac.
What a low cost per TB does not tell you
Cost per TB ranks capacity value. It says nothing about whether the drive survives, how fast it writes, or whether it suits the job, and those gaps decide real purchases.
Reliability varies by model, not by price band. Backblaze publishes failure data from its fleet of hundreds of thousands of drives, and its 2025 Drive Stats report put the fleet-wide annual failure rate at 1.36%, with wide gaps between individual models. A cheap-per-TB model with a poor failure record is expensive storage once a rebuild or a lost backup enters the ledger.
Recording method matters for sustained writes. CMR drives hold their write speed under long transfers; SMR drives can slow sharply once their cache fills, which is why NAS and surveillance buyers check the recording type before the $/TB. Speed class matters too: a 7,200 RPM drive or any SSD costs more per terabyte because it finishes work faster, and for a boot drive or an editing scratch disk that trade is usually worth it. If your comparison drifts from drives to subscriptions, price the recurring side separately with the Azure storage pricing calculator, which models cloud tiers rather than hardware you own.
What competing calculators miss
The cost per TB tools and storage TCO pages reviewed for this article divide a price by a capacity and stop, or swing to the opposite extreme and model an entire data center. The gaps in the middle are where home and small-office buyers actually decide.
Miss 1: electricity never appears. A simple divider treats a drive that sleeps in a drawer and a drive spinning 8,760 hours a year as the same purchase. Over a five-year life at $0.17 per kWh, a 6 W drive burns $44.68 of electricity, close to the entire sticker price of a budget 4 TB drive. The true yearly cost mode here prices that line in.
Miss 2: one drive at a time. Single-drive tools force two runs and mental subtraction to compare a shortlist. This tool compares two drives in one pass and states the saving per TB per year, which is the figure a buyer can act on.
Miss 3: enterprise TCO machinery for a two-drive question. Full storage TCO calculators add PUE, cooling, failure-rate replacements, and RAID overhead. Those inputs matter in a rack; for a home NAS they bury the answer. This page keeps exactly the terms that move a small decision: price, lifespan, watts, rate, and capacity.
Frequently Asked Questions
There is no fixed fair price, because storage prices move quickly. Compare drives of the same type and capacity class in the same week: large consumer hard drives have recently landed roughly between $15 and $45 per TB depending on whether they are desktop or NAS models, while SSDs cost several times more per terabyte. The right test is relative: the lower $/TB wins on capacity value, and warranty and recording type break ties.
Enter terabytes. If a drive is sold in gigabytes, divide by 1,000 first: a 500 GB drive is 0.5 TB, and a 2,000 GB drive is 2 TB. Use the advertised capacity on the box, not the smaller figure an operating system reports.
Manufacturers count 1 TB as 1,000,000,000,000 bytes (decimal), while Windows measures in binary units, properly called tebibytes, and labels them TB. A 4 TB drive therefore shows about 3.64 TiB. You received every byte you paid for; only the ruler changed.
No. Cost per TB ranks capacity value only. Warranty length, reliability record, CMR versus SMR recording, rotational speed, and whether the drive is rated for your use (desktop, NAS, surveillance, or enterprise) can each outweigh a small $/TB gap.
Yes. Commas are stripped before the math runs, so entering 1,200 for an 8 TB drive returns $150.00 per TB, the same as entering 1200.
It prices one year of ownership per drive: price divided by lifespan in years, plus electricity (watts times 24 times 365, divided by 1,000, times your rate per kWh), then divides the total by capacity. In the pre-filled example, drive A costs $5.62 per TB per year against drive B at $6.73, so A wins by $1.12 per TB per year.
Yes, with one care point: enter the price for a defined period and read the result as cost per TB for that same period. A $20 monthly plan offering 2 TB returns $10.00 per TB per month. Recurring subscription pricing is not directly comparable with a one-time drive price until you also compare time periods.
Add This Calculator to Your Website
References
- National Institute of Standards and Technology, “Prefixes for Binary Multiples”: the standard definitions of kibi, mebi, gibi, and tebi behind the TB versus TiB gap. NIST: Prefixes for Binary Multiples. Accessed October 2026.
- Seagate Technology, “Storage Capacity Measurement Standards”: why drive makers report capacity in decimal units and how operating systems report it differently. Seagate: Storage Capacity Measurement Standards. Accessed October 2026.
- Backblaze, “2025 Year-End Drive Stats Report” announcement: annualized failure rate of 1.36% across more than 344,000 drives, with model-level variation. Backblaze: 2025 Drive Stats Report. Accessed October 2026.
- US Energy Information Administration, “Does EIA publish electric utility rate, tariff, and demand-charge data?”: where published US electricity price data comes from, for checking the rate used in true yearly cost mode. EIA: Electricity Rate Data FAQ. Accessed October 2026.
- How-To Geek, “Windows Is Lying to You: Why Your 2TB Drive Only Shows 1.8TB”: a plain-language walkthrough of the decimal versus binary reporting mismatch. How-To Geek: Why Your Drive Shows Less Space. Accessed October 2026.