Conversion Rate Optimisation

9 min read

Conversion Rate Optimisation

The practice of increasing the percentage of visitors who complete a desired action --- usually a purchase.

What is it?

Conversion rate optimisation (CRO) starts with an uncomfortable truth: most people who visit a website leave without doing the thing the business wants them to do. In e-commerce, the average conversion rate sits between 2% and 3%.1 That means for every 100 visitors, 97 or 98 walk away. CRO is the discipline of understanding why they leave and systematically fixing it.

The “conversion” in CRO is whatever action matters most to the business: making a purchase, signing up for a newsletter, requesting a demo, or creating an account. The “rate” is simply the percentage of visitors who complete that action. If 1,000 people visit a product page and 30 buy, the conversion rate is 3%.

What makes CRO powerful is that small improvements compound dramatically. Moving from a 2% conversion rate to a 3% rate does not sound like much, but it is a 50% increase in revenue from the same traffic. The business does not need to spend a single extra euro on advertising --- it just needs to fix the friction that is turning visitors away.2

The primary tools of CRO are the conversion funnel (tracking where visitors drop off at each stage), A/B testing (comparing two versions of a page to see which performs better), and user research (understanding why people behave the way they do). The Baymard Institute, which has studied e-commerce checkout usability for over a decade, has found that 70.22% of online shopping carts are abandoned before purchase --- and that 35% of that abandonment is caused by fixable checkout design problems.3

In plain terms

CRO is like running a shop where 97 out of 100 people walk in and leave without buying. Instead of spending more to get even more people through the door, you figure out why they are leaving and remove the obstacles. It is almost always cheaper to fix the shop than to buy more foot traffic.

At a glance

How does it work?

The funnel: where visitors drop off

Every conversion follows a sequence of steps --- the funnel. In e-commerce, the typical funnel is: visit the site, browse products, add something to cart, begin checkout, complete purchase. At each stage, a percentage of people leave.1

CRO begins by measuring the drop-off rate at each stage. If 60% of visitors browse but only 15% add to cart, the gap between browsing and carting is the biggest opportunity. If 15% add to cart but only 2% purchase, cart abandonment is the problem to solve.3

Think of it like...

The funnel is like water flowing through a series of pipes with holes. You do not fix all the holes at once --- you find the biggest leak and patch it first. That single repair can have a dramatic effect on how much water reaches the end.

Checkout friction: the 70% problem

The Baymard Institute’s research on cart abandonment reveals that 70.22% of shopping carts are abandoned before purchase. Their analysis of the reasons breaks down as follows:3

ReasonPercentage
Extra costs too high (shipping, tax, fees)48%
Site requires account creation26%
Delivery too slow23%
Doesn’t trust site with card information25%
Checkout process too long or complicated22%

Many of these are design problems, not product problems. A business can lose nearly a quarter of its potential customers simply because the checkout form has too many steps. Baymard estimates that 35% of abandonment is recoverable through better checkout design alone.3

Think of it like...

Imagine a customer in a physical shop, item in hand, walking to the till --- and then the cashier asks them to fill in a form, create a membership card, and wait in a separate queue. Many would put the item down and leave. Online checkout friction works exactly the same way, except the customer can leave with a single click.

Concept to explore

See cart-abandonment for a deeper look at why customers abandon carts and the specific design patterns that recover them.

A/B testing: measuring what works

CRO is not guesswork. The primary method is A/B testing --- showing one version of a page (A) to half of visitors and a modified version (B) to the other half, then measuring which version produces more conversions.2

For example, a business might test whether a green “Buy now” button outperforms a red one, whether a one-page checkout converts better than a three-step checkout, or whether showing customer reviews on the product page increases purchases.

The discipline is in testing one change at a time, running the test long enough to reach statistical significance, and resisting the urge to implement changes based on opinion rather than data.

Think of it like...

A/B testing is like a restaurant trying two different menus to see which one sells more. Monday through Wednesday, half the tables get menu A. Thursday through Saturday, the other half get menu B. At the end of the month, the data shows which menu drove more orders --- not which one the chef personally preferred.

Why do we use it?

Key reasons

1. It multiplies existing traffic. Doubling the conversion rate has the same revenue effect as doubling the traffic --- but costs far less. A business that improves from 2% to 3% conversion gets 50% more revenue without increasing its marketing budget.1

2. It reduces effective customer acquisition cost. When more visitors convert, the cost per customer drops. If you spend 10,000 euros on advertising and convert 200 customers, your CAC is 50 euros. Improve the conversion rate so that the same traffic produces 300 customers, and your CAC drops to 33 euros --- with no change in ad spend.2

3. It compounds over time. Every CRO improvement is permanent (until something breaks it). A checkout redesign that lifts conversion by 0.5% delivers that lift every day, on every visitor, for as long as the design is live. Over a year, the cumulative impact is enormous.3

When do we use it?

  • When traffic is healthy but revenue is below expectations (the visitors are there, but they are not buying)
  • When cart abandonment rates are high (above 60-70% for e-commerce)
  • When acquisition costs are rising and the business needs to extract more value from existing traffic
  • When launching a new product page, checkout flow, or landing page
  • When A/B testing infrastructure is in place and the business has enough traffic to reach statistical significance

Rule of thumb

If you are spending money to drive traffic and fewer than 3% of visitors convert, CRO should come before any increase in ad spend.

How can I think about it?

The leaky shop

Imagine you own a shop where 100 people walk in every hour and only 2 buy something. Your first instinct might be to put up a bigger sign outside to attract more people. But you already have 98 people who walked in and left --- something inside the shop is wrong.

Maybe the layout is confusing and people cannot find what they want. Maybe the prices are hidden and people do not want to ask. Maybe the queue at the till is too long and people give up. CRO is the practice of observing those 98 people, understanding why they left, and fixing the shop so that 3, 4, or 5 of them stay and buy.

You do not need more foot traffic. You need to fix the leaks.

The leaky pipe

Think of your website as a pipe carrying water (visitors) from one end (the landing page) to the other (the purchase confirmation). The pipe has holes at every joint: the product page, the cart, the checkout form, the payment step.

You could increase water pressure (spend more on ads to drive more traffic). But if the pipe is full of holes, most of the extra water leaks out before it reaches the end. CRO is the practice of finding and sealing those holes.

The smartest businesses fix the pipe first, then increase the pressure. They get more output from the same input --- and every repair is permanent.

Concepts to explore next

ConceptWhat it coversStatus
cart-abandonmentWhy customers add items to cart and leave before purchasingcomplete
customer-journey-mappingTracing the full path from awareness to purchase and beyondstub
customer-acquisition-costThe total cost to gain one new paying customercomplete
customer-lifetime-valueThe total revenue a customer generates over the full relationshipcomplete

Some cards don't exist yet

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Where this concept fits

Position in the knowledge graph 

graph TD
    MS[Marketing & Sales] --> CRO[Conversion Rate Optimisation]
    MS --> CLV[Customer Lifetime Value]
    MS --> CAC[Customer Acquisition Cost]
    MS --> CJM[Customer Journey Mapping]
    CRO --> CA[Cart Abandonment]
    CJM --> CRO

    style CRO fill:#4a9ede,color:#fff

Related concepts:

  • customer-lifetime-value --- CRO increases the number of customers from the same traffic, which improves CLV economics across the business
  • customer-acquisition-cost --- higher conversion rates reduce effective CAC without changing marketing spend

Sources

Further reading

Resources

Footnotes

  1. Littledata. (2025). Average Ecommerce Conversion Rate. Littledata. ↩ ↩2 ↩3

  2. VWO. (2025). What Is Conversion Rate Optimization (CRO)?. VWO Blog. ↩ ↩2 ↩3

  3. Baymard Institute. (2026). 49 Cart Abandonment Rate Statistics. Baymard Institute. ↩ ↩2 ↩3 ↩4 ↩5

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