A conversion is only as trustworthy as its precision. Show too few digits and you lose accuracy; show too many and you imply a certainty the measurement never had. Here’s how to think about it.
Significant figures in one minute
Significant figures are the digits that carry real information. In 12.30, all four digits are significant; the trailing zero says the value is known to hundredths. In 0.00450, only 4, 5, and the final 0 are significant — the leading zeros just place the decimal point.
When you convert a measurement, the result should not claim more significant figures than the input. Converting “about 5 miles” to “8.04672 kilometres” is misleading precision — “8 km” or “8.0 km” is honest.
Round at the end, not the middle
The most common accuracy mistake is rounding partway through a calculation. Each rounding step introduces a small error, and chaining them compounds it. Best practice: keep full precision through every intermediate step and round only the final answer. Units Verse does exactly this — calculations run at full double precision and only the display is rounded. See our methodology.
Choosing a precision
- Everyday use (cooking, travel, DIY): 1–2 decimal places is plenty.
- Engineering and trade: match the precision of your least-precise input.
- Scientific work: carry the significant figures your instrument justifies, and note the uncertainty separately.
Every converter on Units Verse has a precision control so you can dial in exactly how many decimal places to display — from a clean whole number up to ten places — without affecting the underlying value.
Exact vs. measured values
Some conversion factors are exact by definition (1 inch is defined as exactly 2.54 cm), so they don’t limit significant figures. Others are measured constants with their own uncertainty. When exactness matters — see our sources — start from the definitional value rather than a rounded one.