Hello, I think what I am trying to do is called weighted average in Excel, but I can not figure it out. I have a temperature reading at random times. I would like to calculate the average temperature over the entire time set. example; Time Temp 11:07 35.1 11:15 31.6 11:28 29.3 11:38 28.6 11:48 28.4 11:58 28.3 12:18 28.2 12:48 28.6 13:08 28.3 13:28 28.6 What would the weighted average temperature be over the entire time set?

I don't think what you want is a weighted average. Here is a definition of "weighted average": http://www.investorwords.com/5854/w... and here is an Excel example: http://www.meadinkent.co.uk/xlwtdav... I don't see where you have the required proportional relationship between the temperatures required to determine the weighted average. I could be wrong...

Do you mean you want the Average Temperature? Assuming the temperatures are in their own column (B for this example) In Cell B11, you'd want =AVERAGE(B1:B10) Pretty simple. "So won’t you give this man his wings What a shame To have to beg you to see We’re not all the same What a shame" - Shinedown

Pretty simple...except that I'm not sure the OP is looking for a simple average. The OP specifically mentioned that the reading times were random. As an extreme example, if a reading were taken every minute for 3 hours then =AVERAGE() would be pretty accurate. However, if 1 reading was taken at 12:01, another at 12:02 and a final reading at 2:59, I wouldn't be as confident that the average of those three readings would accurately represent the average temperature over the 3 hours.

You might find the interval between reading and use it for the weighting factor of the average temperature of the interval.

Perhaps not, but Average is average, is it not, DD? :) "So won’t you give this man his wings What a shame To have to beg you to see We’re not all the same What a shame" - Shinedown

Ms. Sumn, I'm not sure if you were kidding or not, so I'll respond. No, Average is not Average. - Let's take a portfolio of 3 investments. - Let's invest $100 into each investment. If the 3 investments earn 1%, 2% and 3%, respectively, then the average return of each investment is SUM(1,2,3)/3 = 2% or $6. However, the weighted average return of the same portfolio if the original investment of $300 was split up differently could be higher or lower. For example, invest $50 in the 1% investment, $100 in the 2% investment and $150 in the 3% investment. In that situation, you would gain 2.33%, or $7, on the same $300 starting amount. Therefore, the average temperature over a given time period might not be the same as the weighted average temperature over that same time preiod. Unfortunately, I don't think there is enough data given in the OP to determine anything except the average temp.