Your return on ad spend, and the ROAS you need for the profit you want.
ROAS = revenue ÷ ad spendROAS needed = 1 ÷ (margin before ads − target net margin)One above your break-even ROAS, and that depends on your margin. With a 50% margin you break even at 2.0; with 25% you need 4.0.
No. ROAS compares revenue with ad spend only. ROI also takes out product, shipping and fees, so it is always lower.
The revenue from the ads, for the same dates as the spend. In Ads Manager that is the purchases conversion value.
Ads take 1 ÷ ROAS of every sale; what your margin leaves after that is your net margin. A 60% margin and a 20% target need 1 ÷ 0.40 = 2.5.