How to Calculate Cost per Terabyte

A 2TB drive at £89 can look cheaper than a 4TB drive at £149, but that does not mean it is better value. If you want to know how to calculate cost per terabyte, the key is to ignore the headline price for a moment and work out how much storage you are getting for every pound spent.

That one number - usually shown as £/TB - makes storage comparisons much clearer. It helps when you are choosing between HDDs and SSDs, comparing different capacity options in the same product range, or checking whether an Amazon deal is genuinely worth buying. It is not the only thing that matters, but it is the quickest way to filter out poor-value listings.

The basic formula is simple:

Cost per terabyte = price ÷ capacity in terabytes

If a drive costs £120 and offers 4TB of storage, the calculation is:

£120 ÷ 4TB = £30 per TB

If another drive costs £90 and offers 2TB, that works out as:

£90 ÷ 2TB = £45 per TB

So even though the second drive is cheaper overall, the first one gives you more storage for your money. That is why £/TB is often more useful than sticker price when you are comparing products.

This works across most storage categories. You can use it for internal hard drives, external hard drives, SATA SSDs, NVMe SSDs, USB flash drives and memory cards. The formula stays the same. What changes is how much weight you should give to it.

Storage pricing is full of distractions. A drive might be shown with a large percentage discount, but still be poor value compared with another model nearby. A 1TB SSD may look attractively priced because the total cost is low, yet the 2TB version can often be much cheaper per terabyte.

This matters most for buyers who need bulk capacity. If you are backing up family photos, storing games, building a Plex library or filling a NAS, paying close attention to £/TB can save a surprising amount. Across an 8TB, 12TB or 16TB purchase, even a difference of £4 or £5 per TB adds up quickly.

It also helps stop misleading comparisons between product types. An HDD will usually beat an SSD on cost per terabyte. An NVMe drive will often be the most expensive per terabyte of the three. That does not mean HDD is always the right buy. It means you need to know when value means lowest £/TB and when it means paying more for speed, size or convenience.

Here is where the formula becomes genuinely useful.

Say you are comparing three products:

A 4TB external HDD at £84 A 4TB SATA SSD at £196 A 4TB NVMe SSD at £228

The £/TB figures are:

£84 ÷ 4 = £21/TB £196 ÷ 4 = £49/TB £228 ÷ 4 = £57/TB

From a pure storage value perspective, the hard drive is clearly cheapest. If your goal is long-term backup or media storage, that may be the best buy. But if you are upgrading a gaming PC or need faster scratch storage for video editing, the SSD or NVMe option may still be worth the higher cost per terabyte.

That is the trade-off. Cost per terabyte tells you what you are paying for capacity. It does not tell you what you are paying for speed, noise levels, power use, shock resistance or form factor.

The biggest mistake is comparing different capacities without doing the maths. Many shoppers see a 1TB SSD at £54 and a 2TB model at £94 and assume the smaller one is the better deal because it is less expensive. In reality:

£54 ÷ 1TB = £54/TB £94 ÷ 2TB = £47/TB

The 2TB model costs more upfront but offers better value per unit of storage.

Another common mistake is mixing up terabytes and gigabytes. If a drive is listed as 500GB, that is 0.5TB for simple comparison purposes. So a 500GB SSD at £32 works out at about £64/TB. If you compare that with a 2TB SSD at £96, the larger drive comes in at £48/TB and is the better value option.

A third mistake is ignoring usable capacity. Manufacturers advertise decimal capacity, while operating systems often show slightly less formatted space. For most product-to-product comparisons, listed capacity is fine because all brands are using the same convention. But if you want maximum precision, especially at lower capacities, bear in mind that real usable space will be a bit lower.

£/TB is especially helpful when you are buying storage mainly for capacity. That includes backup drives, external archive drives, desktop hard drives, surveillance drives, and many NAS setups where total space matters more than raw speed.

It is also useful for spotting the best capacity tier in a product family. Manufacturers do not price every size proportionally. One capacity may be oddly expensive, while the next step up is much better value. This is common with SSDs, where 1TB, 2TB and 4TB versions can have noticeably different £/TB figures.

For UK shoppers comparing Amazon listings, this can save time. Instead of manually flipping between tabs and trying to remember prices, you can reduce each option to one comparable number.

Knowing how to calculate cost per terabyte is useful, but it should not be treated as the only buying metric.

If you are buying a boot drive, game drive or workstation drive, speed matters. A cheap HDD with a superb £/TB figure will still feel slow for Windows, large game installs or 4K editing caches. In those cases, a more expensive SSD can be better value in real-world use even with a worse £/TB number.

Reliability and intended use matter too. A bargain desktop drive may look tempting for NAS use, but it may not be rated for that workload. A NAS drive with a higher cost per terabyte may still be the smarter buy if it is designed for multi-bay use, vibration tolerance and longer duty cycles.

Condition also matters. Refurbished and renewed drives can have very attractive £/TB pricing. Sometimes that is a good deal. Sometimes the warranty, usage history or seller quality makes it less appealing than the numbers suggest. A low £/TB figure is only useful if the product itself suits your risk tolerance.

The most practical approach is to use cost per terabyte as your first filter, then narrow by drive type and use case.

If you need the cheapest way to store lots of files, focus on HDDs and sort by lowest £/TB. If you need fast internal storage, compare SSDs or NVMe drives against each other instead of against hard drives. If you need an external backup drive, compare external models by £/TB first, then check brand, warranty, connection type and whether the enclosure matches your setup.

This is where a comparison-led view helps more than reading marketing copy. A drive can be well priced within its own category while still being overpriced against similar products. Equally, the cheapest model is not always the one to buy if it uses an awkward form factor, has weak reviews, or sits in a capacity bracket that is usually poor value.

As a rule, compare like with like first. HDD versus HDD, SATA SSD versus SATA SSD, NVMe versus NVMe. Then look at capacity bands. A 4TB model may be good value, while the 2TB and 8TB versions from the same range are not.

Watch for unusually expensive small capacities. Lower-capacity SSDs and memory cards often look affordable, but their £/TB figure can be far worse than larger models. Also watch for temporary discounts that bring premium brands close to budget-brand pricing. That is often where the strongest value appears.

If you want a shortcut, TerabytePrices tracks this kind of comparison by capacity, drive type, brand and current pricing, which makes it easier to spot whether a listing is merely cheap or genuinely good value.

The useful habit is not just doing the formula once. It is using it every time you compare storage. Once you start thinking in £/TB, confusing listings become much easier to read, overpriced capacities stand out immediately, and buying decisions get faster. That is usually when storage shopping stops feeling like guesswork and starts feeling like a simple numbers problem.