Amplitude vs Google Analytics: Product Events or Ad Traffic

The short answer: if your questions start after signup (activation, a first project, an upgrade) and the product sends under 2 million events a month, Amplitude's Free plan covers it with no card and one year of data access; at 10 million events its Plus estimator showed $576 a month billed annually, or $720 billed monthly (Amplitude pricing, checked on 26 October 2026). If your questions end at the visit and the ad click, and Google Ads bids on your conversions, Google Analytics is free of charge and designed to work with Google's advertising tools. My view: for a product-led company the useful split is both, GA4 on the marketing site and Amplitude inside the product.

Disclosure: I may earn a commission through some links on this site. It does not change what this page says.

Before anything gets tagged twice:

1. Turn users into events. For example, 40,000 monthly active users firing 45 events each send 40,000 x 45 = 1,800,000 events a month, inside Amplitude's free 2 million, and at 5 million the Plus estimator showed $225 a month billed annually (Amplitude pricing). On GA4, a one-quarter exploration at 5 million events a month queries 15 million events, past the 10 million at which standard properties start sampling (GA4 data sampling).
2. Start from the GA4 property you already have. Its key events are what marketing reports on today. Amplitude's work starts where they stop, so the first Amplitude event worth defining is the one that follows the last GA4 key event: the signup confirmation, the first project, the invite.
3. Pick one number both tools will see. Weekly signups works, because both tools see the same form. Record it in both for four weeks before anyone presents either figure. A gap that holds steady is a definition gap; a gap that moves is a tracking fault.

The two are built around different units. GA4 counts sessions and users on a site and hands conversions to Google's ad products. Amplitude counts events tied to a device or a user ID and builds funnels, retention and cohorts from them.

How each one produces its numbers

Read on 26 October 2026: Amplitude's pricing page, Browser SDK docs and MCP docs; Google's cookie usage, Consent Mode overview, data sampling, behavioural modelling, data retention, EU data and privacy and MCP server pages.

Where they differ in practice

Where the question starts

A growth lead asking which channel brings visitors who sign up asks a GA4 question. The same lead asking which signups go on to invite a colleague within a week asks an Amplitude question, because the answer lives in events after login, tied to a user ID set at signup. The Amplitude how-to builds that activation funnel step by step.

What a number means once people say no

Article 5(3) of the ePrivacy Directive allows storing or reading information on a visitor's device only with consent after clear and comprehensive information, apart from what is strictly necessary for a service the user asked for. Both tools store identifiers in cookies by default, which is the kind of storage that article covers. What happens after a refusal differs. Amplitude's SDK documents an opt-out flag: refusers are simply absent from the data. Google's Consent Mode in its Advanced form sends cookieless pings while consent is denied, and GA4 can model the missing users, but only once a property meets the thresholds in its modelling article. The banner set-up, the Dutch rules and the questions for counsel are in consent-friendly EU analytics.

How exact, and for how long

GA4's standard reports keep their history, but explorations and funnels only see user and event data for 2 or 14 months on a standard property, with 26 to 50 months reserved for 360, per its retention article. Amplitude's Free plan gives one year of data access and Plus two, per its pricing page. A year-on-year cohort comparison fits both only if GA4 is set to 14 months.

Price points from each vendor

From Amplitude's bill estimator on its pricing page and Google's Analytics page, checked on 26 October 2026. Growth and Enterprise are priced by Amplitude's sales team, and Analytics 360 by Google's. Startups under $10 million in funding with fewer than 20 employees can apply for a free year of Amplitude Growth.

One agent step: the same number from both, side by side

Connect both MCP servers to one assistant: Amplitude's, which works on every plan, and Google's, which runs locally, needs Python 3.10 or higher and a Google Cloud project, and can only read. Ask for weekly signups for the last four weeks from each, as a two-column table. Amplitude's server can also create and edit charts, so ask for reads only; its docs say deletes ask for confirmation first. A person then checks the definitions behind each column before trusting the gap: which GA4 key event and which Amplitude event, which time zone, and whether either count includes people who refused consent.

Choose Amplitude if the job is

• Finding which behaviour in the first week predicts an upgrade.
• Retention and cohort analysis on logged-in users of a SaaS product or an app.
• Experiments and session replay on the same events, from the free tier up.

Choose Google Analytics if the job is

• Reporting traffic and conversions on a marketing site.
• Feeding conversions to Google Ads bidding.
• Analytics with no event bill, where the budget for tools is zero.

Free on both, then the default to trim

Both start free, and that is enough to answer the first question. Put GA4 on the site, Amplitude Free in the product, and run the four-week signup comparison from the list above.

Then read Amplitude's init code before you go live. Its Browser SDK switches on page views, sessions, form interactions, file downloads and attribution unless the code turns them off (Browser SDK docs), and once volume passes the free 2 million, every one of those defaults is billable volume on a per-event plan, including page views GA4 already records for nothing. Switch off what GA4 covers.

Later, once both tools agree on how many people signed up and the argument turns to which campaign caused them, a causal attribution tool such as Causality Engine is built for that question (disclosure: I founded it).

FAQ

Can Amplitude replace GA4 for Google Ads?

Not on the documentation read. Google's Analytics page lists Google Ads, Search Ads 360 and Display & Video 360 as products it is designed to work with, while Amplitude's pricing page lists campaign reporting with 2 channel views on Free and Plus.

Does Amplitude's free plan run out?

No. Its pricing FAQ calls Free a plan rather than a trial, with 2 million events a month, no card and no time limit.

Will both tools report the same signups?

Rarely. Identity (a cookie against a user ID), consent handling, time zones and modelling all differ, as set out above. Expect a steady gap and investigate a moving one.