Units, sig figs & uncertainty
How it worksConvert units, get your significant figures right, and work out the uncertainty in a result.
In every unit
Count and round
Calculate with sig figs
× and ÷: the answer keeps the fewest significant figures. + and −: it keeps the fewest decimal places. For mixed calculations, do one step at a time.
The rules, quickly
- Non-zero digits always count:
4.56has 3. - Zeros between digits count:
4.06has 3. - Leading zeros never count:
0.0045has 2. - Trailing zeros count after a decimal point:
4.50has 3. - Trailing zeros in a whole number are unclear:
4500has 2 to 4. Write4.50 × 10³to show 3.
Uncertainty in a calculated result
💾 Everything is worked out in your browser.
How it works & questions
How it works
- 1
Convert units
Pick from 18 kinds of unit, from length and pressure to energy and viscosity.
- 2
Get the sig figs right
Count significant figures, round to the right number, and follow the rules for calculations.
- 3
Work out uncertainty
Propagate measurement uncertainty through a formula for your lab report.
Questions
How are significant figures counted?
Non-zero digits always count, zeros between them count, leading zeros don't, and trailing zeros count only after a decimal point. The tool shows which digits count.
How is uncertainty propagated?
By adding uncertainties in quadrature (the usual method), or the worst case if you prefer. The working is shown.
Does it work offline?
Once the page has loaded, everything runs in your browser.