Thamani pH
Thamani pH ni skeli inayoonyesha kiwango cha asidi katika dutu fulani. "pH" ni kifupi cha Kilatini "pondus Hydrogenii" (Kiingereza "potential of Hydrogen").
Skeli hii ina thamani kuanzia 0 hadi 14. Namba ndogo inaonyesha tabia ya kiasidi, namba kubwa tabia ya kibesi. Dutu isiyo na tabia ya besi wala asidi huwa na thamani pH ya 7. Asidi huwa na kiwango chini ya 7, besi njuu ya 7.
Mifano ya thamani pH
hariri| pH | |
| Asidi ya betri | 1.0 |
| Asidi ya tumboni | 2.0 |
| Majimaji ya Limau | 2.4 |
| Cola | 2.5 |
| Siki | 2.9 |
| Maji ya chungwa au tofaa | 3.5 |
| Bia | 4.5 |
| Kahawa | 5.0 |
| Chai | 5.5 |
| Mvua asidia | < 5.6 (hadi 2.5) |
| Maziwa | 6.5 |
| Maji tupu | 7.0 |
| Damu | 7.34 - 7.45 |
| Maji ya bahari | 8.0 |
| Sabuni | 9.0 - 10.0 |