What does TBW mean on an SSD?

TBW is terabytes written: a volume of data the maker specifies the drive for, usually alongside the warranty term. It is a written quantity rather than a statement of how long the drive will work.

Three published figures get bundled together as though they meant the same thing. This one is a volume.

What the TBW specification states

TBW states an amount of data written to the drive, expressed in terabytes. The maker specifies the drive against that volume, generally under a defined workload pattern, and generally alongside a warranty term.

It scales with capacity. Larger drives of the same model usually carry a proportionally larger figure, because there is more flash to spread writing across and the controller’s wear levelling has more room to work. That is the single most useful thing to know about it: comparing the TBW of a small drive against that of a large one from the same range is comparing capacities.

Why the figure exists at all

Flash cells wear with writing. Each one tolerates a finite number of program-and-erase cycles, and the controller spends its life spreading writing evenly so that no small part of the drive is worn out while the rest is untouched.

TBW is the maker’s statement of what the drive is built for, given that mechanism. It is meaningful, it is comparable between drives, and it is one of the few endurance figures that is specific to the model rather than to a population.

What it is not

It is not a countdown to failure. Drives are not specified to stop at the figure, and a drive can fail long before it for reasons that have nothing to do with wear — a controller fault, a power event, a manufacturing defect.

It is not a duration. Converting it into years requires knowing how much is written per day, which is a property of your usage rather than of the drive. Two identical drives in two machines will reach the figure at completely different times.

It is not the same as the warranty term, though the two are printed together. Many warranties end at whichever arrives first, and the maker states that condition in its own terms.

How to work out whether it matters to you

Find out how much your machine actually writes in a day. Operating systems and drive utilities report a written total, and watching it for a week gives a realistic figure that no rule of thumb will.

For most desktops and laptops, ordinary use is nowhere near the specified volume over any plausible ownership period. The cases where it genuinely matters are the ones where writing is the job: a cache for video work, a database, a machine recording continuously, or a drive used as a scratch volume.

The three figures, kept apart

TBW is a written volume. MTBF is a statistic about a population under stated conditions. Warranty length is a commercial undertaking with its own conditions. They are published separately because they describe separate things, and none of the three answers the question of how long the drive in front of you will work.

That is not an evasion — it is why a second copy of anything that matters lives somewhere other than the drive.

The manufacturer’s own documentation comes first, and this page is not a substitute for it. Every rate, capacity, class figure, endurance rating, port speed and power figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A stated capacity is reported as the maker counts it, and is never restated in another unit, because the two are not the same figure. And for anything sold with a lifespan implied: TBW, MTBF and warranty length are three different published figures, and none of them is how long a drive will last. TBW is a written volume, MTBF a population statistic, a warranty a commercial undertaking with its own conditions. They are published separately because they describe separate things.