Half-Life Calculator

Enter any values; everything else updates automatically.
Inputs
λ is shown in per sec; T and τ use the same time unit as t.
sec
sec
per sec
sec
Step-by-step derivation
References
  • Remaining quantity: N(t) = N(0) · 0.5^(t/T)
  • Exponential form: N(t) = N(0) · e^(−λ·t) = N(0) · e^(−t/τ)
  • Relations: T = ln(2)/λ = τ·ln(2)
  • Rearrangements: t = T·log₂(N(0)/N(t)), λ = ln(2)/T, τ = 1/λ

More of our calculators...

Atom Calculator

Use our Atom Calculator to relate atomic number, mass number, charge, protons, neutrons and electrons. Fast, accurate, ideal for chemistry and physics.

Theoretical Yield Calculator

Compute theoretical yield from limiting reagent and stoichiometry. Units auto-convert, live updates, step-by-step, PDF export — by Ajax Calculator.

PPM to Molarity Calculator

Convert ppm to molarity and back with molar mass & density. Live syncing, step-by-step derivation, and PDF export. Ajax Calculator.

pH Calculator

Free pH calculator that syncs [H+], [OH−], pOH, concentration, and mass/volume. Supports strong/weak acids and bases, unit options, steps, and PDF.

Molarity Calculator

Calculate molarity fast from mass, volume, molar mass, and mass concentration. Live updates, unit conversions, and PDF export. Free online by Ajax Calculator.

Avogadro’s number calculator

Calculate moles, particles, mass and molar mass using Avogadro’s constant. Real-time results with unit selectors and PDF export; mobile-friendly.