Why does my 1TB drive only show 931GB?

Because of two different ways of counting. Drive makers sell a terabyte as a trillion bytes, but your operating system often measures in units of 1024, which makes the same drive display as about 931GB. No space is missing, it is just two ways of labelling the same capacity.

Is my drive faulty if it shows less than advertised?

No, this is completely normal and every drive does it. A 1TB drive showing roughly 931GB, or a 2TB showing about 1.81TB, is exactly as expected. Nothing is wrong and no space has been lost.

Does formatting reduce a drive's capacity?

A tiny amount, yes, for the file system's own bookkeeping, but the main difference you see is the counting units, not formatting. The bulk of the gap between advertised and shown capacity is the trillion-versus-1024 measurement difference.

Why Is My Hard Drive Smaller Than Advertised?

Published: August 6, 2026

Live answer · Amazon.com

Pulling live prices…

📊 As of August 29, 2026, the typical HDD (10TB+) on Amazon.com is $42.91/TB or $0.043/GB, widest choice around $28.75/TB, with some as cheap as $21.59/TB across 1123 live listings.

Sourced from real discussions on r/techsupport and r/buildapc, cross-checked against live PricePerGig listings.

I’ve been scammed, my new 8TB drive is actually only 7.2TB, that’s 800GB less than I thought I was getting. For every 1TB you buy, you only get 931GB!

Nobody likes to be short changed, and to be honest I’ve always thought it was a bit of a scam, but it’s the industry. You do know ‘bigger numbers’ means better right? so if you’re a manufacturer and you want the ‘biggest’ but physics is actually against you, what do you do… let the marketing team figure it out.

And so it is, what is actually 1 KB (1024 bytes) is considered just 1000 bytes on the front of the box. Think of it like buying chicken - some ‘manufacturers’ pump it full of water so when you get to the till, you’re buying a heavier item, even though the actual weight of the chicken is less - that’s why when you first put it in the pan sometimes it looks like you’re boiling the chicken in water instead of frying it, and let’s not get onto the DNA stripped ‘white powder’ that they also put in the water to actually make it stay in there, I digress. Needless to say, it happens with your food, it happens with hard drives, someone wants to sell you something that cost nothing, and in this case, every Operating System counts a single KB as 1024 bytes, but every hard drive manufacturer counts it as 1000 bytes.

The table above shows the live price per TB for hard drives of 10TB and up on your marketplace, where this gap is at its most noticeable, and where knowing it changes nothing about which drive is best value.

The two ways of counting

Here is the whole mystery, solved.

Drive manufacturers measure a terabyte as a clean trillion bytes. One thousand times one thousand times one thousand, and so on. Nice and decimal.

Your operating system, on the other hand, often counts in units of 1024. So it takes that same trillion bytes and divides differently, which makes a 1TB drive display as roughly 931GB.

Same drive. Same bytes. Two different labels. Nothing has vanished.

It happens to every drive

This is not a trick or a fault, and it is not just your drive.

A 1TB drive shows about 931GB.
A 2TB drive shows about 1.81TB.
A 4TB drive shows about 3.64TB.

Every drive from every brand does exactly this. The bigger the drive, the bigger the apparent gap, but the percentage is always the same. It is simply the counting difference, showing up consistently.

What about formatting?

People often blame formatting, so let me clear that up too.

Formatting does take a tiny sliver of space for the file system’s own record keeping. But it is small.

The big difference you notice, the 1TB to 931GB jump, is almost entirely the counting units, not formatting. So do not worry that you formatted something wrong. You did not.

Why it matters when buying

Here is the practical upshot for your wallet.

Because every drive loses the same percentage to this counting quirk, it does not change which drive is best value. A drive advertised at the best price per TB is still the best value after the units shake out.

So compare drives on their advertised capacity and price per TB, like the live table above shows, and buy normally. Just set your real-world expectations a little lower than the box says.

The bottom line

Your drive is not smaller than advertised and nothing is broken. A 1TB drive showing 931GB is just two ways of counting the very same bytes, and every drive does it.

Expect roughly that bit less usable space than the label, compare drives on price per TB using the live table above, and buy with confidence. The missing space was never missing at all.

So for every 1TB you buy, you’re short changed 69GB, and as drives get bigger and bigger, you really start to notice this, it’s just the industry. the main thing is that pricepergig also counts the same 1000GB is 1TB, and so all the prices are worked out just right for you to compare across the industry.

The two ways of counting

It happens to every drive

What about formatting?

Why it matters when buying

The bottom line

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