Your question is a bit vague, but if you're concerned about using the correct number of sig figs in a calculation you should 'follow the rules'. That is, in multiplication & division you can not have more sig figs in your answer than the least number of sig figs in the data. I always suggest that you carry out the calculation using all of the available data and then round off the answer to meet the rule. For example, if you had the following data: 6.25, 7.895, 12.12345 and you were to multiply these three together you would use all of the given data and get 598.216 You are limited to 3 sig figs (by the value 6.25), so you would record your result as 598.
