Enter your Kb, pKb, Ka, or pKa value into the pKb Calculator, select what you'd like to calculate, and get your pKb alongside related values like Kb, pKa, and Ka — with optional temperature adjustments for more precise results.
pKb
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Kb
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pKa
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Ka
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At 25°C, pKa + pKb = 14 for any conjugate acid-base pair. This relationship comes from the water ionization constant (Kw = 1.0 × 10⁻¹⁴).
pKb is calculated as the negative logarithm of Kb: pKb = -log(Kb). For example, if Kb = 1.8 × 10⁻⁵, then pKb = -log(1.8 × 10⁻⁵) = 4.74.
A higher pKb value indicates a weaker base. Since pKb = -log(Kb), a larger pKb means a smaller Kb, which corresponds to less base dissociation.
For a conjugate acid-base pair, Ka × Kb = Kw = 1.0 × 10⁻¹⁴ at 25°C. This means that knowing one constant allows you to calculate the other.
Yes, pKb can be negative for very strong bases where Kb > 1. However, most weak bases have positive pKb values between 1 and 14.
Temperature affects the water ionization constant (Kw). At 25°C, Kw = 1.0 × 10⁻¹⁴, but it changes with temperature, affecting the pKa + pKb = 14 relationship.