what incline on a the treadmill would you consider uphill

i am new to MFP and want to make ure I am logging my activity correctly. I have been walking on the treadmill (since I live in Pa and it is to cold to walk outside) and I have been logging my pace (3.5mph) and loging it as uphill since i set the incline at2 or above(today to get extra burn i alternated between 2 and 5incline) so the question is is there an incline on the treadmill that would be the minimum setting to be considered uphill. Thanks for the help