The Total Bytes Written to a device over its life can be estimated using the formula shown above. Ideally this would be the usable device capacity times the endurance, the number of times the device can be programmed. However, since there is Write Amplification Factor, the engineer must de-rate this ideal number by the anticipated write amplification factor. In typical applications, there is a WAF range from four to eight. However, WAF is highly dependent on the host system write behavior. Therefore, in some cases, writes are small and random, WAF can be much higher. Highly sequential write behavior can achieve a much more efficient WAF that is close to one. From the formula, note that TBW would be increased if the engineer increased the endurance and / or increased device capacity. TBW is sometimes referred to as teraBytes written.