Quick Answer
- Trailing zeros after the decimal point are significant — 0.50 has 2 sig figs, 0.500 has 3.
- Leading zeros before the first non-zero digit are not significant — 0.060 has 2 sig figs.
- All non-zero digits and zeros between them are always significant — 1.504 has 4 sig figs.
Count Sig Figs Instantly — Free
Enter any decimal and the calculator shows the sig fig count with a step-by-step breakdown.
Open Sig Figs Calculator →The most common source of confusion in significant figures is decimal trailing zeros. Write 0.5 and you have one sig fig. Write 0.50 and you suddenly have two — even though the values are mathematically equal. That extra zero is not decoration: it signals that you measured to the hundredths place, not just the tenths. Understanding this one rule resolves most “how many sig figs” questions for decimal numbers.
This guide gives direct answers for the numbers most commonly searched — 0.50, 0.250, 1.50, 0.060, and more — with step-by-step walkthroughs showing exactly which digits count and why. For the full set of sig fig rules (including arithmetic and rounding), see the complete significant figures guide.
Advertisement
Quick Reference — Common Decimal Sig Figs
The table below covers the numbers that appear most often in homework, lab work, and online searches. Use it as a quick lookup before checking the worked examples below.
| Number | Sig figs | Significant digits | Key rule applied |
|---|---|---|---|
| 0.50 | 2 | 5, 0 | Trailing zero after decimal IS significant |
| 0.250 | 3 | 2, 5, 0 | Trailing zero after decimal IS significant |
| 1.50 | 3 | 1, 5, 0 | Trailing zero after decimal IS significant |
| 0.060 | 2 | 6, 0 | Leading zeros NOT significant; trailing zero IS |
| 0.500 | 3 | 5, 0, 0 | Both trailing zeros after decimal ARE significant |
| 1.20 | 3 | 1, 2, 0 | Trailing zero after decimal IS significant |
| 0.00250 | 3 | 2, 5, 0 | Three leading zeros NOT significant; trailing zero IS |
| 45.5147 | 6 | 4, 5, 5, 1, 4, 7 | All digits significant — no leading zeros |
| 0.5 | 1 | 5 | No trailing zero written — only 1 sig fig |
| 1.5 | 2 | 1, 5 | No trailing zero written — only 2 sig figs |
The 3 Rules That Cover Every Decimal
Every decimal significant-figures question is answered by one of these three rules. Learn them once and you can count sig figs in any number without a calculator.
| Rule | Applies to | Significant? | Example |
|---|---|---|---|
| Rule 1 | Non-zero digits (1–9) | Always | 0.25 → 2 and 5 are both significant |
| Rule 2 | Leading zeros (before first non-zero digit) | Never | 0.060 → the 0 and first 0 after decimal are not significant |
| Rule 3 | Trailing zeros after the decimal point | Always | 0.250 → trailing 0 is significant; 1.50 → trailing 0 is significant |
Tip: There is no Rule 4 for pure decimals. The only ambiguous case is trailing zeros in whole numbers without a decimal point — e.g., 500 could have 1, 2, or 3 sig figs. When a decimal point is present (0.50, 1.50), all ambiguity disappears.
How Many Sig Figs in 0.50?
Answer: 2 significant figures.
| Digit | Position | Significant? | Reason |
|---|---|---|---|
| 0 | Before decimal | No | Leading zero — placeholder only |
| 5 | Tenths | Yes | Non-zero digit — always significant |
| 0 | Hundredths | Yes | Trailing zero after decimal — always significant |
The trailing zero in 0.50 is significant because it was written deliberately. If the measurement were only precise to the tenths place, you would write 0.5, not 0.50. The extra zero communicates that the hundredths digit was measured and found to be zero.
How Many Sig Figs in 0.250?
Answer: 3 significant figures.
| Digit | Position | Significant? | Reason |
|---|---|---|---|
| 0 | Before decimal | No | Leading zero — placeholder only |
| 2 | Tenths | Yes | Non-zero digit — always significant |
| 5 | Hundredths | Yes | Non-zero digit — always significant |
| 0 | Thousandths | Yes | Trailing zero after decimal — always significant |
The common mistake is treating the trailing zero in 0.250 as a placeholder and saying it has 2 sig figs. It has 3, because 0.250 ≠ 0.25 in a scientific context — the extra zero means you measured to the thousandths place.
How Many Sig Figs in 1.50?
Answer: 3 significant figures.
| Digit | Position | Significant? | Reason |
|---|---|---|---|
| 1 | Ones | Yes | Non-zero digit — always significant |
| 5 | Tenths | Yes | Non-zero digit — always significant |
| 0 | Hundredths | Yes | Trailing zero after decimal — always significant |
1.50 has no leading zeros, so every digit is evaluated only by Rules 1 and 3. The 1 and 5 are significant by Rule 1 (non-zero). The trailing 0 is significant by Rule 3 (trailing zero after decimal). Total: 3.
How Many Sig Figs in 0.060?
Answer: 2 significant figures.
| Digit | Position | Significant? | Reason |
|---|---|---|---|
| 0 | Before decimal | No | Leading zero — placeholder only |
| 0 | Tenths | No | Leading zero — before first non-zero digit |
| 6 | Hundredths | Yes | Non-zero digit — always significant |
| 0 | Thousandths | Yes | Trailing zero after decimal — always significant |
0.060 is the trickiest of the common examples because it has both leading zeros (not significant) and a trailing zero (significant). The first zero before the decimal and the zero in the tenths place are both leading zeros — they are just locating the decimal point. Once you reach the 6 (the first non-zero digit), all remaining digits including the trailing zero are significant.
Rounding to N Significant Figures
Some questions ask not just how many sig figs a number has, but what it looks like rounded to a specific count. The process: identify the Nth significant digit, look at the digit immediately after it, and round up if that digit is 5 or more.
| Number | Round to | Result | How |
|---|---|---|---|
| 45.5147 | 4 sig figs | 45.51 | 4th sig fig is 1; next digit is 4 → round down |
| 45.5147 | 3 sig figs | 45.5 | 3rd sig fig is 5; next digit is 1 → round down |
| 45.5147 | 2 sig figs | 46 | 2nd sig fig is 5; next digit is 5 → round up |
| 0.00250 | 2 sig figs | 0.0025 | 2nd sig fig is 5; next digit is 0 → round down |
| 1.50 | 2 sig figs | 1.5 | 2nd sig fig is 5; no further digits → stays 1.5 |
| 0.250 | 2 sig figs | 0.25 | 2nd sig fig is 5; next digit is 0 → round down |
Tip: When rounding removes trailing zeros (e.g., 1.50 rounded to 2 sig figs becomes 1.5), the result has fewer sig figs than the original — that is expected and correct. The sig figs calculator above shows rounded results automatically.
More Examples: 0.500, 1.20, and 0.00250
The same three rules from above apply to all of these:
| Number | Sig figs | Explanation |
|---|---|---|
| 0.500 | 3 | 0 (leading, not sig) + 5 (sig) + 0 (trailing, sig) + 0 (trailing, sig) = 3 |
| 1.20 | 3 | 1 (sig) + 2 (sig) + 0 (trailing after decimal, sig) = 3 |
| 0.00250 | 3 | 0.00 (three leading zeros, not sig) + 2 (sig) + 5 (sig) + 0 (trailing, sig) = 3 |
| 0.5 | 1 | 0 (leading, not sig) + 5 (sig) — no trailing zero written = 1 |
Open Sig Figs Calculator — Free
Paste any number or expression and get the sig fig count with a step-by-step digit breakdown.
Open Sig Figs Calculator →