Hong Life CalculatorsUnderstanding the SSD endurance (TBW and DWPD) calculator — concept and principle
Flash memory cells wear out after a limited number of program/erase cycles, so SSD makers rate how much data can be written over the warranty period. This calculator converts a drive's rated terabytes written (TBW) into an expected life for your daily write volume, and expresses the same rating as drive writes per day (DWPD). It is used when choosing between consumer, read-intensive and mixed-use drives.
How it is calculated
- Expected life (years) = TBW × 1000 ÷ (daily host writes in GB × write amplification) ÷ 365.
- DWPD rating = TBW ÷ (capacity in TB × 365 × warranty years).
TBW and capacity are in decimal terabytes; 1 TB = 1000 GB. Write amplification (WAF) is the ratio of data written to flash to data sent by the host.
The principle
TBW is the total amount of data the vendor promises the drive can absorb within its warranty. Dividing it by how much you write each day gives the number of days until that budget is used up. The SSD actually writes more to flash than the host sends, because it must move valid data during garbage collection; the WAF factor here scales your daily writes to represent a workload harsher than the one the rating assumed. DWPD restates TBW as "how many times the full capacity can be written every day for the warranty period", which makes drives of different sizes comparable.
Worked example
- Inputs: TBW 600 TB, capacity 1 TB, 50 GB/day, WAF 1, warranty 5 years.
- Effective daily writes: 50 × 1 = 50 GB. WAF 1 is the default because TBW ratings under JESD219 are already stated in host writes.
- Days of life: 600 × 1000 ÷ 50 = 12,000 days.
- Years: 12,000 ÷ 365 = 32.88 years. With WAF 1.5 it would be 21.92 years.
- DWPD: 600 ÷ (1 × 365 × 5) = 0.329.
| Writes per day (GB) | Expected life (years) |
|---|---|
| 12.5 | 131.5068493 |
| 25 | 65.75342466 |
| 37.5 | 43.83561644 |
| 50 | 32.87671233 |
| 62.5 | 26.30136986 |
| 75 | 21.91780822 |
| 100 | 16.43835616 |
How to read the result
If the expected life is well beyond the warranty, endurance is not your limit; the warranty years or other failures will come first. Ratings around 0.3 DWPD are common for consumer drives, about 1 DWPD for read-intensive enterprise drives and about 3 for mixed-use. Write-heavy servers, video recorders and caching layers are the cases where TBW really matters.
Common mistakes
- Applying WAF on top of a rating that already reflects your workload; use 1 if your workload resembles the vendor's rating workload.
- Mixing GB and GiB or TB and TiB.
- Treating TBW as the point of failure; drives often last beyond it, but the warranty ends there.
Frequently asked questions
How do I find how much I write per day?
Read the drive's SMART data (for example "Data Units Written" on NVMe) twice some days apart and divide by the days.
Does a larger SSD last longer?
Usually yes for the same flash type, because TBW tends to scale with capacity and writes spread over more cells.
What happens when TBW is reached?
Nothing immediately; the drive keeps working until cells fail, but the warranty may end.
Sources: JEDEC JESD218, Solid-State Drive (SSD) Requirements and Endurance Test Method · JEDEC JESD219, Solid-State Drive (SSD) Endurance Workloads