Tips for counting sig figs?

[Brianna Martilla 1C]

I am working on week 1 homework, question 4, and I am quite rusty on counting significant figures. Does anyone have any tips or ways they remember? thanks

[Sabina House 2A]

If a number has decimal places, it usually has the same amount of sig figs as digits in the number. For example, 4.00, 40.2, and 5.46 all have 3 sig figs because they all have 3 digits. However, in a number like 0.029, there are no digits present before the 2, so this value would only have 2 sig figs because the zeros in this case are only placeholders for the decimal value. The number 0.0290 would have 3 sig figs because the last 0 in this number is not just a placeholder, it is added on the end to have a meaning. In numbers without decimals that start and end with a number other than 0, they have the same number of sig figs as digits. For example, 309 and 423 both have 3 sig figs. If a number ends with 0, this is not the case. For example, 6370 would only have 3 sig figs because the last 0 is just a place holder for the size of the number. The number 502,800 would have 4 sig figs because the last two zeros at the end of the number are just placeholders. To summarize, zeros are counted as sig figs when in between other numbers (309, 3.402) or at the end of numbers after the decimal point (3.40, 4.00). Zeros are not counted as sig figs when before numbers after the decimal point if no other numbers are before these zeros (0.029) and at the end of values without decimals (6370). Sorry if this was confusing but I hope it helps some!

[Marisa Gaitan 2D]

In general, you will count numbers after a decimal place as another sig fig. So for example, in that homework problem, 4.000 has 4 sig figs. 11020 only has 4 sig figs because there is no decimal after the final 0. You generally also do not count zeros if there is no number preceding it. So 0.006 only has 1 sig fig, 0.030 has 2. Dr. Lavelle has a link on his 14a website to other sig fig rules regarding addition, subtraction, multiplication, etc.

[Samuel Flores 1E]

I think it's easiest to summarize the sig fig rules into 3 simple steps that determines whether the number is significant or not:
1. If the number is nonzero (3, 6, 8, etc.), then it is a significant figure.

2. If the number zero is in between two non zero numbers (606, 802, etc.), then it is a significant figure.

3. If trailing zeros follow a decimal (7.000, 6.3400, etc.), then it is a significant figure.
- If those trailing zeros do not follow a decimal (79,000, 860, etc.), then it is not a significant figure.

By following these rules, and with practice, then you should get used to counting sig figs.

Hope this helps!

[David Chibukhchian 2G]

I agree with the other answers to this question, and would maybe add that it's important to remember that the rules for adding and subtracting sig figs are different than for multiplying or dividing them. When adding and subtracting sig figs, the number with the lowest amount of digits after the decimal point determines how many digits after the decimal point the answer will have. For example, if you're adding 2.14 to 6.72915, your answer would be written as 8.87, with two digits after the decimal point. In this case, since 2.14 had the lowest number of digits after the decimal point, it determines how many your answer will have (two). I hope that helps and makes sense a little!

[Darlene Lien 3E]

Hi, in case you wanted to refer back to tips for sig figs, you could visit Dr. Lavelle's website! There's a pdf titled "Everything you want to know about sig fig" explaining sig figs in depth. Hope this helps!

[Jayasree Peri 2J]

Another tip for counting sig figs that helped me was the Atlantic-Pacific rule.
Basically, the central decider to how you count your sig figs is the decimal point. The P in Pacific refers to present (there is a decimal point), and the A in Absent refers to Absent (there is no decimal point). If there is a decimal point, you start counting from the first nonzero number from the left side of the number. If there is no decimal point, you start counting from the first nonzero number from the right. Below is a visual representation of this rule.

Examples:
• 245000: no decimal point --> start counting from Atlantic side (the right) --> 3 sig figs
• 245.000: decimal point --> start counting from Pacific side (the left) --> 6 sig figs

[clairehathaway 2J]

I agree with the other answers to this question, and would maybe add that it's important to remember that the rules for adding and subtracting sig figs are different than for multiplying or dividing them. When adding and subtracting sig figs, the number with the lowest amount of digits after the decimal point determines how many digits after the decimal point the answer will have. For example, if you're adding 2.14 to 6.72915, your answer would be written as 8.87, with two digits after the decimal point. In this case, since 2.14 had the lowest number of digits after the decimal point, it determines how many your answer will have (two). I hope that helps and makes sense a little!

Yes I think this is super important to remember! Adding/subtracting has to do with the number of decimal points, paying no attention to the numbers preceding the decimal point. So 2.3498 + 1874567.8 would have an answer of 1874570.2, with only one number after the decimal point. Whereas with multiplication/division you pay attention to the total number of digits. So 23.4 x 1351.986432 would have an answer of 31600, with a total of 3 sig figs.

[905290504]

if the decimal is present start with from the left side of the number and counts the figures starting with the first nonzero figure. Everything to the right of that is also significant. If the decimal is absent start from the right and start counting sig figs once you hit your first nonzero. everything to the left of that is also significant.
hope this helps!

[Brianne Conway 1D]

I think it's easiest to summarize the sig fig rules into 3 simple steps that determines whether the number is significant or not:
1. If the number is nonzero (3, 6, 8, etc.), then it is a significant figure.

2. If the number zero is in between two non zero numbers (606, 802, etc.), then it is a significant figure.

3. If trailing zeros follow a decimal (7.000, 6.3400, etc.), then it is a significant figure.
- If those trailing zeros do not follow a decimal (79,000, 860, etc.), then it is not a significant figure.

By following these rules, and with practice, then you should get used to counting sig figs.

Hope this helps!

Thanks a lot! I was also having trouble remembering how to count significant figures and you explained it succinctly and understandably. I'll definitely remember this from now on when counting sig figs.