Precision desk01

Significant figures,
fully explained.

Count, round, and calculate with confidence. Every answer includes the rule that fired, the limiting value, and the working behind it.

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Enter a number or expression

The calculator detects whether you want to count, round, or solve an expression.

0.00456 3 sig figs

0.00456

Significant figures

0.00456 has 3 significant figures.

The five counting rules

Rule	Significant?	Example
Non-zero digits	Always	`123` → 3
Captive zeros (between non-zeros)	Always	`4008` → 4
Leading zeros	Never	`0.00456` → 3
Trailing zeros with a decimal point	Yes	`1.200` → 4
Trailing zeros, no decimal point	Ambiguous	`1200` → 2 (write `1.200×10³` for 4)

Operation rules

Operation	Rule	Example
Addition / subtraction	Result keeps the fewest decimal places of any term.	`41.34 + 1.561 = 42.90`
Multiplication / division	Result keeps the fewest significant figures of any factor.	`2.5 × 3.42 = 8.6`
Multi-step	Keep guard digits; round only at the final step.	`(2.0 + 3.0) × 4.00 = 20`
Exact numbers	Counted or defined values have infinite significant figures and never limit the result.	`π, 100 (defined)`

Purpose-built tools7 calculators

Choose the exact job

Focused tools make the rule visible, preserve meaningful zeros, and show alternate notation.

Count & map

Sig Fig Counter

See exactly which digits count and why zeros behave differently.

Convert notation

Scientific / E-Notation Converter

Move between decimal, scientific, E, and engineering notation.

Fix decimal places

Round to N Decimal Places

Keep the requested place value, including meaningful written zeros.

Compare modes

Rounding Mode Comparator

Put six rounding methods side by side on the same input.

Round precisely

Round to N Significant Figures

Round to any number of significant figures with method-aware working.

Check conventions

Convention Switcher

Compare classroom, exam, standards, and software conventions.

Explore every calculator

Desk reference5 core rules

Which digits are significant?

Read a number from left to right. The location of a zero—not the zero itself—decides whether it carries precision.

01Non-zero digits

Always significant

4.56 → 3 SF

02Leading zeros

Placeholders only

0.0045 → 2 SF

03Captive zeros

Always significant

1.008 → 4 SF

04Decimal trailing zeros

Significant

2.300 → 4 SF

05Integer trailing zeros

Ambiguous without context

1200 → 2–4 SF

Operation rulesKnow the difference

The operation chooses the limit

+ −

Addition & subtraction

Match the fewest decimal places.

12.11 + 0.3 = 12.4

× ÷

Multiplication & division

Match the fewest significant figures.

4.56 × 1.4 = 6.4

Our standardTransparent by default

A result should never be a black box.

Each tool identifies the governing rule and retains guard digits until the final step. When conventions can change an answer, we make the difference visible.

Compare conventions

Significant figures,fully explained.