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Half-life
What is left after a time, or how long since there was more, with the mean life too
It runs entirely in this browser tab: the numbers you type are never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page.
What it takes
- Starting amount
- A value you supply.
- Left over
- Leave it out and the tool works it out from the others.
- Half-life
- A value you supply.
- Time elapsed
- Leave it out and the tool works it out from the others.
An example
initial = 100
half_life = 5730
elapsed = 11460
Settings
- Half-lives in the table
- How far the halving table runs; each row is half the one above it. A number from 2 to 20.
How to use it
- Fill in the boxes above. Anything you leave blank the tool works out.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Can I build from this?
- Not from this alone. The cable, beam and rainwater tools each say so on their own result: they are arithmetic, and what may be built is decided by the wiring, structural and water regulations where the work is — none of which this page has read.
- Why does a tool refuse a number it could clearly calculate?
- Because several of these formulas are fits rather than laws. Wind chill is defined at 10 °C or colder in a wind over 4.8 km/h, the heat index from 27 °C up, and the barometric formula to the top of the troposphere. Outside those the arithmetic still runs and the answer means nothing, so the tool says which rather than printing it.
- Does anything here use floating point?
- No. Every figure is exact decimal arithmetic, which is why 0.1 + 0.2 is 0.3 here and a unit conversion comes back to where it started. The one place a ceiling exists — how many digits an exponent may carry — is stated rather than reached silently.
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. A measurement is somebody's experiment and a load is somebody's building; none of it is sent anywhere.
Other tools for in the laboratory
Crystal unit cell
The density a lattice gives, with the atoms per cell and the packing that follow from it
Beer–Lambert law
Absorbance, concentration or path length, with the linear range named
Error propagation
What the uncertainties of the inputs do to the answer, and which one dominates
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