Great question! No. Each line item calculates separately, so you can mix and match if you like. Use whichever metric is best for you, and the calculator will properly convert it to pounds of CO2. Be careful that you are using the metric your data is calculated in, or you could get wildly different results. So, if you have your data. in ‘feet’, make sure you select feet when entering your data. If it is in “meters”, select “meters”, and so on.