When an SSD deal is actually a deal

Divide the price by the capacity in terabytes and compare that figure. Price per terabyte is the one number that stays comparable across sizes. A discount percentage tells you about the list price it was measured against, and a seller chooses that.

How do you compare prices across sizes

Price per terabyte is the price divided by the number of terabytes the drive is sold as. There is no more to the method than that. Use the capacity on the box rather than the smaller figure your operating system reports, and use the same convention for every drive you are weighing up — the comparison only has to be consistent with itself.

The figure ranks price, not value. Two drives can land on the same price per terabyte and differ in the interface they use, in how they behave on a long write, and in what they are rated to endure. So draw up the shortlist first, from the drives that fit your machine and are fast enough for what you do, and use price per terabyte to order what is left. It answers which of two acceptable drives is cheaper per unit of room, and nothing else.

It is also the figure that survives a change of size, which is the part a percentage cannot do. Each capacity is measured against its own reference, so a percentage on a 1 TB drive and a percentage on a 4 TB one are not on the same scale and cannot be put side by side. Two price-per-terabyte figures always can.

Across every SSD we track the capacity sits in the same row as the price, so the division needs nothing you have to go and look up.

Why a good price on one size says nothing about the next

Capacity tiers move on their own, and a move in one is not a signal about the others. Part of the gap between two sizes is structural rather than weather: the largest capacity in a range carries a premium. Sizing an SSD works through where that premium comes from and how to spot it between two sizes. The rest is weather. Two sizes reach their prices for different reasons, and they leave them at different times.

That is how they are treated here. A model sold at several capacities is one product here, but each size carries its own price history, and each size is scored against its own history rather than against the model's. A verdict on one size is not a verdict on the model, and reading it as one is how a drive that is cheap at 1 TB sells you the 2 TB version at no discount at all.

Which makes the order matter. Settle the capacity you intend to live with, then look at what it costs. Starting from whichever size looks best per terabyte this week is how people end up with a drive that is too small at an excellent price.

What a discount percentage is measured against

A percentage is a comparison, and it is worth what the number on the other side of it is worth. Measured against a list price the seller set, it describes the seller. Measured against what the drive has actually been selling for, it describes the market. We use the second, and we state what each score was measured against rather than leave you to assume. How we score deals sets out the rules behind that, including the cases where we show no score at all.

How do you tell when to buy

Compare a price to that drive's own history rather than to the calendar. No month reliably makes flash cheap, and a rule built on one is folklore that costs money: it either holds you off a good price for weeks or talks you into an ordinary one on a date.

The drive's page is where its history is. For the size you have selected it shows its own recorded low, and how many days of history and how many merchants stand behind it. Read the second part before the first. A low drawn from a few days at one seller is a much weaker claim than the same figure drawn from months across several, and it is the depth of the record that decides how much the low is worth knowing.

The judgement after that is short. A price at or near the lowest we have recorded for that size is unlikely to be improved on by much, and waiting for the rest is a poor trade. A price well above it means the drive has been cheaper recently and may be again, though nothing promises it will be. A price with nothing behind it to compare against is not a bargain. It is an unknown, and it should be read as one.

There is also a cost to waiting that no price history shows. If the machine needs the drive now, a fair price today beats a better price in a month you cannot name.

How to choose an SSD puts price last, after what fits, how much room you need, and how fast the drive has to be, which is the order that stops you buying the wrong drive cheaply. Every SSD we track is on one page, and the guided pick puts the same listings in order for you.