Conversion rate calculator

Worked example

1,800 sessions in a month, 36 orders:

Item	Working	Result
Conversion rate	36 ÷ 1,800	2.0%
95% confidence interval	Wilson interval	1.4%–2.8%
Sessions needed for 100 orders	100 ÷ 2.0%	5,000

36 orders is not many, so the true rate lies somewhere around 1.4% to 2.8%. A drop to 1.6% next month is not necessarily a worse page; it may be ordinary noise.

Using conversion rate to judge ads and pages

A conversion rate is not good or bad on its own; compare it with the rate you can afford:

• Minimum conversion rate = cost per click ÷ target CPA. At 9 per click and a target CPA of 360, you need at least 2.5%. If you are at 2.0%, the problem is the page or the traffic, not the budget. Work out target CPA in the max CPA calculator.
• Check conversion rate before raising order value. Add-ons, bundles and free-shipping thresholds lift order value but can lower conversion. Compare contribution per visitor, not order value alone.
• Wide interval, no verdict. If two versions' intervals overlap heavily, you cannot tell them apart yet. Keep collecting.

Common mistakes

• Comparing rates with different denominators. GA4 often uses sessions, ad platforms use clicks or interactions, some reports use unique users. Google Ads divides conversions by ad interactions that can be tracked to a conversion, and one interaction can count several conversions, so the rate can pass 100%. Check the denominator first.
• More conversions than visitors. The calculator shows "—". Usually one order is being recorded twice; check the tracking.
• Acting on a tiny sample. With single-digit conversions the interval is wide; 3% today and 1% tomorrow are both normal.
• Mixing conversion definitions. Add to cart, checkout started and purchase are all called conversions, and their rates differ several times over. Say which one the report counts.

FAQ

How do you calculate conversion rate?

Conversions ÷ visitors × 100%. 36 orders from 1,800 sessions is a 2.0% conversion rate.

What is a normal conversion rate?

It varies widely by industry, price and traffic source, so someone else's average tells you little. Compare it with the lowest rate you can afford instead: cost per click ÷ target CPA.

How big a sample do I need?

There is no fixed number; look at how wide the confidence interval is. At 36 conversions it runs from 1.4% to 2.8%, the top twice the bottom. More conversions narrow it. While two versions' intervals still overlap heavily, hold off on a verdict.