Numford
Significant figures

How many significant figures in 1.0?

1.0 has 2 significant figures.

Significant figures

Non-zero digit. Every non-zero digit is significant.Zero between digits. A zero between two non-zero digits is significant.Leading zero. Leading zeros only fix the decimal point, so they are not significant.Trailing zero after the point. Trailing zeros in a number with a decimal point are significant.Trailing zero, no point. Trailing zeros in a number without a decimal point are not counted. Write 1.00 × 10² to make them count.Digit of a in a × 10ⁿ. In a × 10ⁿ every digit of a is significant, including its zeros. Counted and defined numbers, such as 3 coins or 100 cm in a metre, are exact and have unlimited significant figures.

Tap a digit to see why it counts.

2significant figures
Scientific notation1.0 × 100

Round to

2
significant figures

1.01.0

Nothing is dropped.

Add, subtract, multiply, divide

Add or subtract. The answer keeps as many decimal places as the number that has the fewest. Multiply or divide. The answer keeps as many significant figures as the number that has the fewest. The rounding is done once, on the exact result.
  • 4.2374 significant figures
  • 2.513 significant figures

Exact result1.68804780876

Multiply or divide: keep the fewest significant figures.

Reported1.693 significant figures
The rule used

Digit by digit

  • 1

    Non-zero digit: countsEvery non-zero digit is significant.

  • 0

    Trailing zero after the point: countsTrailing zeros in a number with a decimal point are significant.

Scientific notation

1.0 × 10⁰

  • Rounded to 1 significant figure1
Related

Nearby numbers

Rounding a value? See 2.745 to 3 significant figures.

Questions

1.0: quick answers

How many significant figures does 1.0 have?

1.0 has 2 significant figures. In 1.0, trailing zeros count because there is a decimal point.

Why do the trailing zeros of 1.0 count?

Trailing zeros in a number with a decimal point are significant, because writing them says the measurement was made to that place. 1.0 written as 1.0 × 10⁰ shows all 2 digits.

What is 1.0 rounded to 1 significant figure?

1.0 rounded to 1 significant figure is 1. The first dropped digit is 0, less than 5, so the last kept digit 1 stays.

Count your own number Open error analysis