pH & pOH Calculator

For acid-base chemistry calculations.

Enter any one value to calculate the others. Use 'e' for scientific notation (e.g., 1.5e-5).

Worked Examples: pH and pOH

Example 1: pH from [H+] = 2.5×10−4 M

  1. Formula: pH = −log10[H+].
  2. Compute: pH = −log10(2.5×10−4) = −(log 2.5 − 4) ≈ −(0.398 − 4) = 3.60.
  3. At 25°C, pOH = 14 − pH = 10.40; solution is acidic.

Example 2: pOH from [OH−] = 3.2×10−6 M

  1. Formula: pOH = −log10[OH−].
  2. Compute: pOH = −log10(3.2×10−6) = −(log 3.2 − 6) ≈ −(0.505 − 6) = 5.50.
  3. Then pH = 14 − pOH = 8.50; solution is basic.

Example 3: Find [H+] from pH = 7.25

  1. [H+] = 10−pH = 10−7.25.
  2. Compute: 10−7.25 ≈ 5.62×10−8 M.
  3. Then [OH−] = Kw/[H+] = 1.0×10−14 / 5.62×10−8 ≈ 1.78×10−7 M.