### Rules For Significant Figures

Posted:

**Tue Oct 02, 2018 2:55 pm**Can sombody explain the rules for what is considered a significant figure?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=9&t=32814

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Posted: **Tue Oct 02, 2018 2:55 pm**

Can sombody explain the rules for what is considered a significant figure?

Posted: **Tue Oct 02, 2018 3:04 pm**

I think explaining it would be better through examples.

1.0 has two sig figs

10 has one sig fig, so does 100, so does 2000.

2300 has two sig figs (so numbers before zeros count as sig figs). But if a decimal is placed then the zeros are significant e.g 2300. has 4 sig figs.

0.003 has one sig fig

0.00030 has 2 sig figs

1.0 has two sig figs

10 has one sig fig, so does 100, so does 2000.

2300 has two sig figs (so numbers before zeros count as sig figs). But if a decimal is placed then the zeros are significant e.g 2300. has 4 sig figs.

0.003 has one sig fig

0.00030 has 2 sig figs

Posted: **Tue Oct 02, 2018 3:08 pm**

There was one thing that Dr. Lavelle mentioned in class that really helped me understand how to determine how many significant figures are present in a number. If you are unsure on the amount of significant figures in a number, convert the number into scientific notation. The number of didgets in the first part of the scientific notation will be the number of sig figs! Hope this helped, and best of luck!!

Posted: **Tue Oct 02, 2018 6:15 pm**

I was taught to visualize the United States

If the decimal is present in this number start on the pacific side P. If it is absent, start on the Atlantic side A.

Then from the first non zero digit underline all other digits in that direction. These are the significant figures.

When adding and subtracting, use the least number of decimal spaces, and for multiplying and dividing use the least number of significant figures being used in the calculation.

If the decimal is present in this number start on the pacific side P. If it is absent, start on the Atlantic side A.

Then from the first non zero digit underline all other digits in that direction. These are the significant figures.

When adding and subtracting, use the least number of decimal spaces, and for multiplying and dividing use the least number of significant figures being used in the calculation.

Posted: **Wed Oct 03, 2018 1:25 pm**

So how many sigfigs are there in 705.0090 ??

Posted: **Wed Oct 03, 2018 2:27 pm**

The number 705.0090 would have 7 significant figures based on the rules listed above.

Posted: **Wed Oct 03, 2018 4:44 pm**

These are the rules that I learned and use when determining how many significant figures are in a value:

1. All nonzero digits are significant (ex: 345.23 has 5 significant figures)

2. Zeroes between between two nonzero digits are significant (ex: 103.106 has six significant figures)

3. Zeroes to the left of the first nonzero digit are NOT significant (ex: 0.0008 has 1 significant figure)

4. Zeroes after a decimal point are significant (ex: 45.000 has five significant figures)

5. Zeroes before a decimal point and after a nonzero digit are significant (ex: 2500.00 has six significant figures)

6. I think that the rule for zeroes before an implied decimal point is that they are ambiguous so it's better to just use scientific notation.

Hope this helps!

1. All nonzero digits are significant (ex: 345.23 has 5 significant figures)

2. Zeroes between between two nonzero digits are significant (ex: 103.106 has six significant figures)

3. Zeroes to the left of the first nonzero digit are NOT significant (ex: 0.0008 has 1 significant figure)

4. Zeroes after a decimal point are significant (ex: 45.000 has five significant figures)

5. Zeroes before a decimal point and after a nonzero digit are significant (ex: 2500.00 has six significant figures)

6. I think that the rule for zeroes before an implied decimal point is that they are ambiguous so it's better to just use scientific notation.

Hope this helps!