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First-Order Rate Constant from Half-Life Calculator

k = ln 2 / t½ for first-order kinetics.

Compute the first-order rate constant k of a reaction (or radioactive decay) from its half-life t½: k = ln 2 / t½. Reports k in per-second, per-minute, and per-hour units.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

k = ln 2 / t½

In depth

Compute the first-order rate constant k of a reaction (or radioactive decay) from its half-life t½: k = ln 2 / t½. Reports k in per-second, per-minute, and per-hour units.