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What Is a Conversion Rate, and How Do You Calculate Yours?

Conversion rate is orders divided by sessions, times one hundred. The simple formula hides three decisions - what counts as a conversion, sessions or visitors, and over what period - that change the number.

Published 24 October 2026Evidence checked on 24 October 2026Small online stores, global English edition

The short answer

Your conversion rate is the number of conversions divided by the number of sessions, multiplied by 100 to make a percentage. If 3,000 sessions produced 45 orders, your rate is 1.5 percent. That is the whole formula. The judgement calls sit inside it: what you count as a conversion, whether you divide by sessions or by individual visitors, and what period you measure over. Decide those once, write them down, and never quietly change them - a rate you calculate the same way every month is a management tool; a rate calculated differently each time is a mood.

Sessions or visitors in the denominator

Platforms disagree. Shopify reports conversion rate over sessions; Google Analytics can report over users. One determined buyer who visits four times and buys once is 25 percent by user and one order in four sessions by session. Neither is wrong, but they are not comparable, and comparing your session-based rate to someone else's user-based rate produces nonsense conclusions. Pick the number your platform shows by default, note which it is, and compare only like with like over time.

Count the conversion the page exists for

Every rate needs its conversion named. Store-wide, the macro conversion is the order. On a product page it might be the add-to-cart; on a landing page, the click through to the product or the signup. Quoting a rate without naming its conversion is how meetings go wrong: one person means orders per session, another means add-to-carts per product view, and both think the other is innumerate. The discipline is boring and essential: rate, conversion, denominator, period - four labels on every number you share or save.

Choose a period long enough to be boring

Daily conversion rates on a small store are mostly noise: a handful of orders one day, none the next. Measure over 30 days at minimum, 90 when you can, and compare against the same period shape - a month with a promotion in it is not a clean comparison for a month without one. Weekend-heavy and weekday-heavy businesses should compare whole weeks. The point of a period is to average out the lumps so that a real change has a chance to show through them.

Calculate the step rates too

The overall rate is a product of step rates: product view to add-to-cart, add-to-cart to checkout start, checkout start to order. Illustration: 3,000 sessions, 900 product views is not a step you control in analytics the same way, so use the steps your tools do show. When the overall rate moves, step rates tell you where it moved. An owner who knows their checkout completion rate within a few points owns a diagnostic instrument; an owner who only knows the blended rate owns a weather report.

Three calculation mistakes to avoid

First, mixing traffic sources mid-comparison: adding a new ad campaign changes who arrives, not how the site performs, yet the blended rate moves and the site gets blamed or credited. Second, counting test orders, staff orders and your own browsing in the numbers - filter them where the platform allows. Third, celebrating a rate rise while order volume falls: a rate can improve because the worst traffic stopped coming. Rate and volume travel together or the story is incomplete. Keep both on the same page of your log, always.

A worked calculation, start to finish

Illustration, one month, one store. Sessions: 6,240. Orders: 91. Conversion rate: 91 divided by 6,240, times 100, equals 1.46 percent. Mobile sessions: 4,370 with 48 orders - 1.10 percent. Desktop sessions: 1,870 with 43 orders - 2.30 percent. Checkout starts: 130, so checkout completion is 91 of 130, or 70 percent. Four numbers, and the month's story is already visible: desktop converts at double the mobile rate, and the checkout itself, once started, completes respectably. The mobile gap is where next month's attention goes. That is the entire skill this guide teaches: compute the same small set of rates the same way every month, and let the gaps nominate the work.

Sources and evidence on the record

Evidence basis: Method guide. Any figure quoted is attributed to a named published source listed below; worked examples are labelled illustrations with round numbers, not measurements. Applies when: Before any optimisation work, and every month after

Next on the bench

Bench 01 - Foundations and measurement Conversion Rate Optimisation for Small Stores: Where to Start Conversion rate optimisation, explained for a small store: measure the funnel as it is, fix the leaks the evidence points to, and test changes honestly at small traffic levels. Bench 01 - Foundations and measurement Set a Baseline Before You Change Anything A baseline is the honest before-picture: conversion by device and source over the last 60 to 90 days, written down before any change ships. Without it, every result afterwards is a guess wearing a number. Bench 01 - Foundations and measurement Micro and Macro Conversions: Count the Steps, Not Just the Sale The sale is the macro conversion; the steps that produce it - product views, adds to cart, checkout starts - are micro conversions. Measuring both turns one vague number into a map of where buyers are lost.