pH he yùng-yi̍t chûng Khîn lì-chṳ́ fa̍t-thu ke yit-chúng phêu-thu, ya chhiu-he thûng-sòng yi-ngi song yùng-yi̍t sôn-kán chhàng-thu ke fên-liòng phêu-chún. Liá-ke khái-ngiam he 1909-ngièn yù Tan-ma̍k Sâng-vu̍t Fa-ho̍k-kâ Søren Peter Lauritz Sørensen thì-chhut.
pH ke kie-son kûng-sṳt:
![{\displaystyle {\mbox{pH}}=-\log _{10}\left[{\mbox{H}}^{+}\right]=\log _{10}{\frac {1}{\left[{\mbox{H}}^{+}\right]}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/9236078cc5b31defafb1f56dd0d8ac8ca26bbc98)
Nernst kûng-sṳt:
![{\displaystyle E=E^{0}+{\frac {RT}{nF}}\ln(a_{{\textrm {H}}^{+}});\qquad \mathrm {pH} ={\frac {E^{0}-E}{2.303RT/F}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a8a43f274784fc7655f741c1af648d3ad6f196f3)