Round to 1 Significant Figure
Rounding to 1 significant figure keeps only the single most important digit: 47,386 becomes 50,000, and 0.0047386 becomes 0.005. It answers 'roughly how big is this?' and nothing more — the language of Fermi estimates, headline approximations and order-of-magnitude thinking in physics. All values on this page use standard half-up rounding.
Round to 1 Significant Figure reference last updated · reference source
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What this tool does
Rounding to 1 significant figure keeps only the single most important digit: 47,386 becomes 50,000, and 0.0047386 becomes 0.005. It answers 'roughly how big is this?' and nothing more — the language of Fermi estimates, headline approximations and order-of-magnitude thinking in physics. All values on this page use standard half-up rounding.
How to use the Round to 1 Significant Figure
- Check Number to round: 47386.
- Check Round to: sigfig.
- Check Significant figures: 1.
- Review the Round to 1 Significant Figure result and its exact-value comparison table.
- Verify assumptions before applying the result.
Formula
Round half up at the chosen precision: decimal places count digits after the point, significant figures count digits that carry meaning from the first nonzero digit, and nearest-multiple rounding snaps to a grid such as the nearest 100.
- x
- Number to round
- mode
- Round to
- places
- Decimal places
- figs
- Significant figures
- multiple
- Nearest multiple of
Ties round half up (away from zero for the magnitude shown in most school contexts); financial rounding rules such as banker's rounding are not applied.
Worked example
Round to 1 Significant Figure: Number to round = 47386; Round to = sigfig; Significant figures = 1. Rounding to 1 significant figure keeps only the single most important digit: 47,386 becomes 50,000, and 0.0047386 becomes 0.005. It answers 'roughly how big is this?' and nothing more — the language of Fermi estimates, headline approximations and order-of-magnitude thinking in physics. All values on this page use standard half-up rounding.
Inputs
- Number to round47386
- Round toSignificant figures
- Decimal places2
- Significant figures1
- Nearest multiple of100
Result
- Rounded value5e+4
- As a number50,000
Round to 1 Significant Figure — worked examples
| Number | Rounded |
|---|---|
| 47386 | 5e+4 |
| 44999 | 4e+4 |
| 45000 | 5e+4 |
| 0.0047386 | 0.005 |
| 0.0044 | 0.004 |
| 987654 | 1e+6 |
| 120 | 1e+2 |
| 15 | 2e+1 |
Results explained
- Rounded value
- Rounded value from the formula above. Ties round half up (away from zero for the magnitude shown in most school contexts); financial rounding rules such as banker's rounding are not applied.
- Decimal places
- Decimal places from the formula above. Ties round half up (away from zero for the magnitude shown in most school contexts); financial rounding rules such as banker's rounding are not applied.
Frequently asked questions
Rounding to 1 significant figure keeps only the single most important digit: 47,386 becomes 50,000, and 0.0047386 becomes 0.005. The reference table on this page shows 8 worked examples computed with exactly that rule.
A leading digit followed by exactly 5 is the tie: 45,000 rounds up to 50,000 at one significant figure under half-up, while 44,999 stays at 40,000.
Use it for sanity checks, Fermi problems ('about how many piano tuners are in Chicago?'), and stripping a spreadsheet result down to the one digit you actually trust.
0.0047386 rounds to 0.005. You can verify it in the table on this page, or type any other value into the calculator above.
A question answered with one-significant-figure reasoning, named for physicist Enrico Fermi: 'How many piano tuners are in Chicago?' Decompose it into rough factors — population, households, pianos per household, tunings per year — round every factor to one figure, and the errors mostly cancel, landing within a factor of two or three of the truth. It is the most useful rounding skill in science and business.
No. Banker's rounding (round-half-to-even) is used in some scientific and financial standards to reduce bias over huge datasets, but this page — and the parent rounding calculator — always rounds a halfway value up, which is the convention taught in schools and used for tax forms.
Yes, with one nuance: the engine rounds halves toward positive infinity, so 47.5 rounds up to 48 at the nearest dollar while -47.5 becomes -47. Away from exact halves, negative values round to the nearest candidate just like positive ones.