ROAS, MER, CAC and break-even ROAS explained
Use advertising metrics together instead of optimizing one ratio in isolation.
The useful formula
ROAS is attributed revenue divided by ad spend. MER compares ad spend with total business revenue. CAC divides spend by new customers; CPA and CPL use orders and leads.
What belongs in the inputs
Keep attribution windows and periods consistent. Orders, leads, customers, revenue, and spend should describe the same market and time range.
How to use the result
Break-even ROAS is approximately one divided by gross margin as a decimal. It is a planning boundary, not a profit guarantee, because overhead, returns, and cash timing remain.