Is a bigger hard drive always cheaper per terabyte?

No, and this is the myth worth killing. The received wisdom is that price per terabyte falls smoothly as capacity rises, so the biggest drive is always the best value. It is a clean curve in a slide deck and a bumpy one in a shopping cart. On Amazon.com the cheapest drive at each capacity from 8TB to 20TB usually sits in a rough $25/TB band, and the cheapest 16TB and 20TB routinely land within a dollar or two of each other per terabyte even though the 20TB is two sizes larger. Now and then one size dips well below the band on a single deal, but that knee moves week to week. Capacity sets a rough floor; the actual cheapest drive at each size is decided by which model is on a good price right now, not by how many terabytes it holds.

Why does one capacity sometimes dip below the rest of the band?

Because the knee is set by one specific listing on a good price, not by the capacity itself. Some months a single deal pulls a size well under its neighbours — often an external USB drive with an enterprise HDD inside, priced below the bare internals around it. That is the honest catch: an external is a shuck candidate, not a bare drive you drop straight into a NAS bay, so a like-for-like internal costs more. Other months, like this one, no single deal breaks away and the curve is nearly flat at about $25/TB from 8TB up. Either way the lesson is the same: the mid-range of the price-per-TB curve is set by individual deals, which is exactly why it is worth checking each size rather than assuming the biggest is cheapest.

Should I just buy small used drives to get the lowest price per terabyte?

Only if you have thought about the whole cost. The single lowest price per terabyte on the site today is a 4TB used Seagate Constellation ES.3 at about $12/TB. To build 20TB out of 4TB drives you need five of them. That is five SATA ports, five drive bays, five drives worth of idle power, and five times the annual odds that one dies and you are doing a rebuild. A used enterprise pull can be a genuinely good buy, but per-terabyte price alone hides the bay, power and failure costs that a bigger drive folds into one unit. I wrote about that trade in more detail in the piece on fewer big drives or more small ones.

Will this month's cheapest capacity still be cheapest next week?

Probably not, and that is the point of this page rather than a flaw in it. Every price here is Amazon.com in US dollars, and drive prices move hourly. Some weeks one capacity dips below the band on a single deal; other weeks, like now, the curve is nearly flat and the cheapest drive you can drop in a bay is actually a 4TB. Next week it could be a 16TB on sale, or a 22TB that just dropped. The durable advice is not the number, it is the habit: before you buy, open the page for the capacity you want and the one on either side of it, look at the price per terabyte rather than the sticker price, and buy the knee. The capacity pages update as prices change, so the number is always current even when this article is not.

Which Hard Drive Capacity Is Cheapest Per Terabyte Right Now? Bigger Is Not the Answer (2026)

Q: Which hard drive capacity is cheapest per terabyte right now?

It moves week to week, so the honest answer is a method rather than a fixed number. On Amazon.com the cheapest buyable drive at each capacity from 8TB to 20TB tends to cluster in a rough $25/TB band, with no reliable discount for going bigger — the cheapest 16TB and 20TB usually land within a dollar or two of each other per terabyte. Whichever size dips cheapest in a given week (the value knee) is set by one specific listing on a good price, and it is often an external or shuck candidate rather than a bare internal 3.5-inch SATA drive, so a like-for-like bare internal costs more. If you want a stable reputable-brand figure, our monthly price-per-TB snapshot puts the cheapest reputable new internal drives in the high-$20s per terabyte. The durable move: open the capacity pages for the size you want and the ones on either side, compare price per terabyte, and buy the knee — that number is always current even when a dated table is not.

Ask most people which hard drive is the best value and they will tell you to buy the biggest one you can afford. Price per terabyte falls as capacity rises, so the 20TB beats the 8TB, and you are done. It is repeated so often that nobody checks it against a cart.

So I checked it. Every figure below is Amazon.com in US dollars, pulled on 1 September 2026, and it is the cheapest drive I can actually buy at each capacity, not a list price or a spec-sheet ideal. The product links are affiliate links, which is how this site pays for itself.

The short version: bigger is not cheaper per terabyte right now. The curve does not slope smoothly downward. This month it barely bends at all — it is nearly flat at about $25/TB from 8TB up, and the single cheapest drive you can drop in a bay is a 4TB.

The price-per-TB curve today

Here is the cheapest usable pick at each capacity, and what it works out to per terabyte.

Capacity	Cheapest pick today	Price	Per TB	Condition
4TB	WD Purple	$88.99	$22.25/TB	used
8TB	WD Gold	$209.00	$26.12/TB	used
12TB	HPE Helium (Ultrastar inside)	$299.00	$24.92/TB	used
16TB	Seagate Exos X16	$399.99	$25.00/TB	used
18TB	MDD MaxDigitalData	$449.99	$25.00/TB	used
20TB	MDD MaxDigitalData	$499.99	$25.00/TB	used

Read down the per-TB column and the smooth-curve story falls apart. From 8TB to 20TB the price per terabyte sits in a tight band around $25/TB, give or take a dollar. Capacity barely moves it. The 16TB is $25.00/TB and the 20TB, two whole sizes larger, is also $25.00/TB — identical per terabyte for a drive that holds a quarter more.

The one drive that breaks the band is the smallest. The 4TB at $22.25/TB is the cheapest thing you can drop in a bay this month, and the 8TB at $26.12/TB is the dearest — so going up one size from 4TB to 8TB actually costs you more per terabyte, not less. There is no knee to chase this month, just a flat line with a dip at the bottom end.

Why the curve bends

Two things are going on, and neither is about capacity.

At the small end, the cheapest price per terabyte is always used enterprise pulls. The single lowest number on the whole site right now is a 4TB used Seagate Constellation ES.3 at about $12/TB. There is a steady supply of decommissioned 2TB to 4TB enterprise drives coming off corporate fleets, and that supply keeps their per-terabyte price under almost everything else. It is real, but it comes with a real bill attached that the per-TB number hides, which is the next question below.

In the middle, the number is set by whichever drive is on a good price this week, not by how big it is. Some months a single listing pulls one capacity well below the band — back in August it was an 18TB external, a SanDisk Professional G-Drive with an Ultrastar enterprise HDD inside, priced under the bare 16TB and 20TB internals around it. This month nothing breaks away like that: 12TB through 20TB all land within pennies of $25/TB. There is nothing structural about any one size being cheaper than the next. It is a deal on one model, and a deal on one model is exactly what moves the knee — or, this month, what fails to.

When one capacity does dip on an external, that is the honest catch on the “winner”: an external is a shuck candidate, not a bare internal you drop straight into a NAS bay. If you want a bare internal at that capacity you will pay the band price, around $25/TB. I went through the shucking maths in detail in is shucking still worth it, and the same caution applies here: a great price on an external is only a great price on a bare drive if you are willing to open the box and void the warranty.

What to actually do with this

The takeaway is not “buy 4TB”. By the time you read this the band may have shifted and a 16TB or a 22TB could have dropped below it. The takeaway is the method.

Before you buy, do three things. Open the page for the capacity you were going to buy, and the pages for the size on either side of it. Look at the price per terabyte, not the sticker price, because the sticker price tells you almost nothing about value. Then buy the knee, the capacity where the per-TB number dips below its neighbours — and if the curve is flat, as it is this month, buy the biggest drive at the band price so you spend fewer bays on the same terabytes.

That is the whole trick, and it is why every page on this site sorts by price per terabyte and updates as prices change. The number in the table above was true on 1 September 2026. The number on the cheapest per TB page is true right now, whenever right now is for you.

One last thing, because it is the mistake I see most. Do not chase the absolute lowest number off the top of the list if it means five small drives instead of one big one. That 4TB used enterprise pull at about $12/TB looks unbeatable until you count the five bays, the five lots of idle power, and the five chances a year that one fails and you are rebuilding an array. A single 20TB at $25/TB costs more per terabyte, but it folds five drives’ worth of bays, power and failure risk into one unit. I put numbers on that trade in fewer big drives or more small ones if you want to see the arithmetic.

Buy the knee. Just check where it is first.

Which Hard Drive Capacity Is Cheapest Per Terabyte Right Now? Bigger Is Not the Answer (2026)

The price-per-TB curve today

Why the curve bends

What to actually do with this

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