PH or ph or pH or Ph may be:

• In chemistry, pH is a measure of acidity.
• Also in chemistry, specifically organic chemistry, Ph stands for a phenyl ring.
• Philippines (ISO country code).
• phot (ph), a measurement of illumination.
• In computational complexity theory, PH is the union of all complexity classes in the polynomial hierarchy.
• A grapheme pronounced like "f", often in words derived from the Greek language containing φ.