I have to calculate the population inside 1000m cells. The total population inside the cell in the images below is 2306.


The green is the buffer from a point. The orange falls outside the buffer. The population distribution inside the cell is even and I have to calculate the population for the buffered area and the area outside of it in the cell.
I clipped the buffered layer and made another layer with just the unbuffered area. But I am not sure how to get the population for these.
Area of the cell/1000 * population of the cell
Population of the cell/160000 * area
I calculated the fields using different formulas but the calculated fields were not right (I am bad at math) because when I summarised the fields, the total went way too high even above the overall population that is around 160000.