What does Cost of Sales (COS) mean in marketing?

In digital marketing, you’ll run into plenty of acronyms that can be confusing at first. One of them is COS. What does COS mean, and why does it matter for your marketing strategy?

What is COS (Cost of Sales)?

COS stands for Cost of Sales. In Czech, the same metric is often referred to as PNO (“Podíl Nákladů na Obratu”). It’s one of the key metrics in performance marketing, especially in e‑commerce. This metric shows what percentage of your total revenue you spend on marketing activities. In other words, it tells you how much of each koruna or dollar of revenue your company earns is invested back into advertising and marketing. COS reflects how efficient your marketing spend is.

How is COS calculated?

Calculating COS is quite simple. Divide your total marketing costs by your total revenue and multiply the result by 100 to get a percentage.

COS = (costs/revenue) 100 = [%]*

Here’s a simple example. If a business spends 100,000 CZK on marketing and its total revenue is 1,000,000 CZK, then its COS is:

COS = (100,000/1,000,000) 100 = 10%*

This means that for every 1 CZK you earn, you spend 0.10 CZK on advertising. In other words, a 100,000 CZK investment in marketing that generates 1,000,000 CZK in revenue results in a COS of 10%.

What is a good COS in marketing?

There is no single “correct” COS value. You’ll often hear that the lower the COS, the better. This isn’t always true. What really matters is that you know your margins, the profit you’re aiming for, and how much you can afford to invest in advertising. If you push COS too low by cutting ad spend, your reach can shrink and your revenue may start to fall. Your goal is to keep COS at a level where you can maximise revenue.

Why is COS important?

COS matters because it shows how efficiently you’re spending money on advertising. It also helps you track how successful your campaigns are, identify seasonal trends, and plan future marketing budgets.

How to optimise and improve your COS

If your COS is too high, there are several ways to optimise it:

1. Improve your conversion rate: The more visitors you convert into buyers, the lower your COS will be. You can significantly increase conversions by optimising your website, improving the user experience, or personalising your ads.

2. Target the right audience: Make sure your campaigns are aimed at the right audience. High‑quality, relevant content focused on the right people is more likely to drive purchases and increase revenue.

3. Analyse and optimise your budget: Track and analyse COS values across different channels and optimise your budgets so you invest more in channels with a better COS.

Conclusion

There is no single right way to do marketing. Every business is unique and needs an individual approach. The same goes for COS – it should be tailored to the specific needs of each business, as there’s no universal “right” value. The key to long‑term success is continuous testing, analysis, and adapting your campaigns to current market conditions. Regular COS optimisation and performance reviews will help you find the balance of spend and return that works for your business.