ROAS is revenue divided by ad spend; ACOS is ad spend divided by revenue. They are reciprocals of each other, so a 25% ACOS is a 4x ROAS and a 50% ACOS is a 2x ROAS. Convert between them with ROAS = 1 ÷ ACOS. Neither is better — Amazon reports ACOS by default, most other advertising platforms report ROAS.
The conversion table
10% ACOS = 10x ROAS. 20% ACOS = 5x ROAS. 25% ACOS = 4x ROAS. 33% ACOS = 3x ROAS. 50% ACOS = 2x ROAS. 100% ACOS = 1x ROAS, meaning you spent exactly what you earned.
Because they are reciprocals, a small ACOS improvement at the low end is a large ROAS movement, which is why ROAS can look more dramatic in reporting.
Which one to manage against
Use whichever your team reads without converting in their head. What matters is comparing it against your break-even, not which format you picked.
If you run advertising outside Amazon, standardising on ROAS makes cross-channel comparison easier.
Want this checked on your own account?
The free audit answers this question with your numbers instead of general rules — no Seller Central password needed.
Get my free audit