Significant figures

How many significant figures in 100?

100 has 1 significant figure. Whole numbers that end in zeros are open to doubt. Written 1.00 × 10², the same value has 3 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.

Type a number

Tap a digit to see why it counts.

1significant figure

Scientific notation1 × 10²

Round to

significant figure

1001 × 10²Written as 100 the trailing zeros are open to doubt.

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.
00
Trailing zero, no point: does not countTrailing zeros in a number without a decimal point are not counted. Write 1.00 × 10² to make them count.

Scientific notation

1 × 10²

Nearby numbers

Rounding a value? See 2.745 to 3 significant figures.

Questions

100: quick answers

How many significant figures does 100 have?

100 has 1 significant figure. In 100, trailing zeros with no decimal point are not counted. Whole numbers that end in zeros are open to doubt. Written 1.00 × 10², the same value has 3 significant figures.

Why is 100 open to doubt?

Without a decimal point the trailing zeros are not counted, so 100 has 1 significant figure. To show 2 or more, write it in scientific notation, for example 1.00 × 10².

Can a number have fewer than one significant figure?

No. 100 already has the fewest, 1 significant figure.

Count your own number Open error analysis