MER

Your total revenue divided by your total marketing spend across every channel. MER = Total revenue ÷ Total marketing spend. Where ROAS judges one campaign, MER shows whether all your marketing together is working.

Channel-level ROAS can look healthy while the business still loses money once every ad, agency and tool is added up. MER is the honest, whole-picture number founders use to scale spend with confidence.

In a month you make £40,000 and spend £10,000 across Meta, Google and email. Your MER is 4.0, meaning every £1 of marketing returned £4 of revenue.