Ecommerce Metrics That Matter: Conversion Rate, AOV and CAC Explained

Your store dashboard probably shows 30 numbers. Revenue is up, sessions are down, and some chart labeled “returning customer rate” is flashing orange. Which of these should actually change what you do on Monday?

For most small online stores, the answer is 3 numbers: conversion rate, average order value (AOV) and customer acquisition cost (CAC). Revenue is simply traffic times conversion rate times AOV. Profit depends on whether what you earn from a customer beats what you paid to get them. This guide explains each metric, how to calculate it properly, the levers that move it, and the supporting numbers that keep you honest.

How the 3 metrics fit together

Think of your store as a simple equation:

Revenue = sessions × conversion rate × average order value

If you get 10,000 sessions in a month, convert 2% of them, and the average order is $60, that’s 200 orders and $12,000 in revenue. (These are illustration numbers, not benchmarks.)

Then add the cost side:

Is a new customer profitable? Compare the gross profit they generate with what it cost to acquire them (CAC).

That’s why these 3 work as a set. You can raise revenue by buying more traffic, but if CAC climbs faster than the profit per order, you’re growing into a loss. And you can raise AOV with bundles, but if conversion rate drops, you may end up flat.

If you’re unsure how metrics differ from KPIs, our explainer on KPI vs metric covers how to pick the few that deserve a target.

Conversion rate

What it is: the share of visits (sessions) that end in an order.

Formula: orders ÷ sessions × 100

Shopify, for example, defines its online store conversion rate as the percentage of sessions that resulted in a sale.

What to know before you trust it:

• Sessions aren’t people. One shopper might visit 4 times before buying. Conversion rate by sessions will always look lower than conversion rate by unique visitors.
• Bot traffic and consent drag it around. Bots inflate sessions, and on some platforms sessions are counted only when visitors accept analytics cookies. Shopify, for instance, rolled out a session measurement update from September 21 to 23, 2026 that filters identified bot sessions by default and counts some sessions without a pageview, and it advises treating post-update data as a new baseline. Any platform change like this can shift your conversion rate without a single extra order.
• Compare like with like. Conversion rate varies a lot by traffic source, device and product. Email traffic and paid social traffic behave differently, so segment before you panic.
• In Google Analytics 4, actions you count as important are now called “key events,” and “conversions” refers to actions used for ad campaign measurement. Make sure your purchase event is set up correctly. Our guide to reading GA4 as a business owner explains the reports.

Levers that move it:

• Faster pages, especially on mobile
• Clear product photos, sizing information and honest descriptions
• Visible shipping costs and delivery dates before checkout
• Fewer checkout steps and more payment options, such as digital wallets
• Reviews and clear return policies
• Better-matched traffic, since visitors from a relevant search convert better than broad audiences

Shoppers who leave at checkout are often reacting to surprise costs or friction. Our article on why shoppers abandon carts goes deeper, and conversion rate optimization covers how to test changes properly.

Average order value (AOV)

What it is: the average amount a customer spends per order.

Formula: revenue ÷ number of orders

Be consistent about what “revenue” means. Shopify’s AOV, for example, uses gross sales minus discounts, divided by orders, and excludes post-order adjustments such as returns. Some owners prefer to calculate AOV on net sales after returns. Either is fine as long as you don’t switch definitions between months.

Levers that move it:

• Free shipping thresholds set slightly above your current AOV. Our guide on offering free shipping without losing money shows how to set one.
• Bundles and multipacks that save the customer a little and raise the basket.
• Cross-sells on product and cart pages (“goes well with”).
• Volume or tiered discounts, such as 10% off 3 or more.
• Premium versions shown alongside the standard option.

Watch for: AOV that rises because you lost small orders, not because people bought more. Always check order count alongside AOV.

Customer acquisition cost (CAC)

What it is: how much you spend, on average, to win 1 new customer.

Formula: acquisition marketing spend ÷ number of new customers in the same period

Decide what goes into “spend” and stick to it:

• Paid media CAC counts only ad spend. It’s easy to calculate and useful for comparing channels.
• Fully loaded CAC adds agency fees, tools, creative costs, influencer payments and the share of staff time spent on acquisition. It’s the honest number for deciding whether growth is profitable.

Count only new customers in the denominator. Including repeat buyers makes CAC look better than it is.

Levers that move it:

• Better targeting and stronger creative in paid campaigns
• Pausing channels whose CAC is consistently above what a customer is worth
• Building lower-cost channels: email list growth, SEO, referrals and organic social
• Improving conversion rate, which lowers CAC automatically because the same spend produces more customers

Attribution, meaning deciding which channel gets credit for a sale, is messy. Our guide to marketing attribution models explains the trade-offs, and many owners also track a blended number: total marketing spend ÷ total new customers.

Metric	Formula	What it tells you	Main levers
Conversion rate	Orders ÷ sessions × 100	How well your site turns visits into orders	Speed, product pages, checkout, traffic quality
Average order value	Revenue ÷ orders	How much each order is worth	Bundles, cross-sells, shipping thresholds, tiered pricing
Customer acquisition cost	Acquisition spend ÷ new customers	What each new customer costs	Targeting, creative, channel mix, conversion rate
Gross margin per order	(Revenue − cost of goods) ÷ orders	Profit available before marketing and overhead	Pricing, supplier costs, discount control
Repeat purchase rate	Customers with 2+ orders ÷ all customers	How many customers come back	Email, loyalty, product quality, post-purchase experience
Customer lifetime value	Profit from a customer over the relationship	How much you can afford to spend on CAC	Retention, AOV, margin

The supporting metrics that keep CAC honest

The 3 headline metrics can hide a loss if you ignore margin and retention.

Gross margin per order. A $60 order with a $30 product cost, $8 shipping and $2 in payment fees leaves $20 before marketing. That $20, not the $60, is what pays back your CAC.

Customer lifetime value (LTV). If customers come back, the first order doesn’t have to cover the whole CAC. Calculate LTV on gross profit, not revenue. Our guide to customer lifetime value shows the formulas.

LTV to CAC ratio and payback period. Compare lifetime gross profit with CAC, and track how many months it takes for a customer’s gross profit to repay their acquisition cost. A long payback period ties up cash, which matters a lot for small stores.

Repeat purchase rate. The share of customers who order more than once in a period such as 12 months. If it’s low, your growth depends entirely on paid acquisition.

Return rate and refunds. High returns quietly shrink both AOV and margin.

Key takeaway: Don’t judge CAC against your average order value. Judge it against the gross profit a customer generates over time. A CAC that looks high can be fine for a product people reorder, and a low CAC can still lose money on a thin-margin, one-time purchase.

A worked example

Here’s a simple illustration using made-up numbers for a small store over 1 month:

• Sessions: 20,000
• Orders: 360, so conversion rate is 1.8%
• Revenue: $21,600, so AOV is $60
• New customers: 250
• Acquisition spend: $7,500, so CAC is $30
• Gross profit per order after product, shipping and payment costs: $22

On the first order, each new customer brings $22 in gross profit against a $30 CAC, so the store loses $8 per new customer on day 1. If the average customer places 2 more orders within a year, lifetime gross profit is about $66, and the economics look healthy. If they rarely come back, the store needs to raise AOV or margin, lower CAC, or both.

Now test levers one at a time. A bundle that lifts AOV to $66 at the same margin percentage raises gross profit per order to about $24. A checkout fix that lifts conversion rate to 2% at the same spend brings in more customers, which pulls CAC down. Small changes compound.

Where to start: a weekly metrics routine

1. Fix your tracking. Confirm purchase events and revenue are recorded correctly in your platform and analytics tool, and that test orders are excluded.
2. Pick consistent definitions for revenue, new customers and acquisition spend, and write them down.
3. Build a 1-page weekly view with sessions, conversion rate, AOV, orders, new customers, CAC and gross margin.
4. Segment conversion rate by traffic source and device once a month.
5. Calculate LTV and repeat purchase rate quarterly; they move slowly.
6. Pick 1 lever per metric to test, and run 1 test at a time so you know what worked.
7. Note platform changes, such as new session tracking or bot filtering, next to your numbers so you don’t mistake a measurement change for a business change.

For a broader view of store reporting, including inventory metrics, see our guide to retail analytics, and for marketing-side numbers, marketing KPIs for small business.

The bottom line

Conversion rate tells you how well your site sells, AOV tells you how much each sale is worth, and CAC tells you what each new customer costs. Read them together, with gross margin and repeat purchases in the background, and you’ll know whether to fix the site, the offer or the marketing. Keep definitions consistent, change one thing at a time, and watch the trend rather than any single week.

Sources

• Shopify Help Center: Analytics fields — Shopify’s conversion rate and average order value definitions
• Shopify Help Center: Session measurement update — September 2026 change to session counting and its effect on conversion rate
• Google Analytics Help: Conversions vs. key events — GA4 terminology for key events and conversions