pKb and Kb Calculator

This calculator converts between a base's dissociation constant, Kb, and its logarithmic form, pKb, and works out the matching pKa of the conjugate acid in the same step. Kb values are often tiny numbers written in scientific notation, which makes it hard to compare how strong different bases are; pKb turns that into a small, easier to read number, where a lower pKb means a stronger base. To use it, pick whether you already have Kb or pKb from the "You have" dropdown, then enter your value. If you enter Kb, the calculator returns pKb using pKb equals minus the base ten logarithm of Kb; if you enter pKb, it returns Kb using Kb equals 10 to the power minus pKb. Either way, it shows the matching pKa of the conjugate acid, worked out from pKa plus pKb equals 14 at 25 degrees Celsius, and a plain language description of base strength, from very strong through to very weak. The worked example on this page uses ammonia, with a Kb of about 1.8 times 10 to the minus 5, giving a pKb of about 4.74 and a conjugate acid pKa of about 9.26; enter 1.8e-5 with Kb selected to check it. This tool suits chemistry students, teachers and lab workers who need to convert constants quickly, compare base strength, or work through conjugate acid-base pairs and buffer calculations.

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