The honest opening: the formula is often enough
If your whole need is a live rate in a spreadsheet cell, stop reading and type =GOOGLEFINANCE("CURRENCY:USDEUR"). Free, instant, no install. This page exists for the jobs where that stops being true – and it is specific about where the line sits.
Route 1 – GOOGLEFINANCE: free, capable, bounded
What it does well: live rates ("delayed by up to 20 minutes", per Google's help page), historical rate-on-a-date via the INDEX(...) unwrap, all inside the sheet with zero setup.
Its documented boundaries, which are the actual decision inputs: it exists only in Sheets – Docs, Gmail, Slides and Calendar have no formula engine, so it cannot follow you there; historical data "cannot be downloaded or accessed via the Sheets API or Apps Script" – no automation may read it; Google "cannot guarantee the accuracy of the exchange rates displayed" and tells you to confirm current rates before any transaction they could affect; and the CURRENCY: syntax it all rests on is absent from Google's own documentation – working but unpromised. The troubleshooting guide has every documented failure mode.
Route 2 – your own script: control, for a price
Apps Script calling a real rate API (the ECB's free daily reference feed, or a commercial provider) gets you what GOOGLEFINANCE refuses: automatable rates, your choice of source, your refresh schedule. The price is the build and the care: API keys, a custom function that "must return within 30 seconds" or the cell shows #ERROR!, a daily URL Fetch quota (20,000 calls a day on a consumer account, 100,000 on Workspace), and maintenance forever. Right when rates feed a system; overkill when they feed a human.
Route 3 – an add-on: for the jobs that aren't in a cell
The case for an add-on is mostly about where conversion needs to happen and who is doing it: a quote being written in Docs, an invoice being checked in Gmail, a colleague who should not need formula syntax to answer "what's that in euros". A sidebar that converts on the spot, across the apps where the work already is, is a different tool from a formula – not a better formula.
The decision table
| Job | Use |
|---|---|
| Live rate in a sheet cell | GOOGLEFINANCE |
| Rate-on-a-date for an invoice column | GOOGLEFINANCE, then paste-values |
| Rates feeding a script or pipeline | Your own script + a rate API (GOOGLEFINANCE is blocked here) |
| Converting while writing a Doc, email or slide | Add-on – no formula engine exists there |
| Colleagues converting ad hoc, no syntax | Add-on |
| Audit-grade or trading-grade rates | None of these – Google says to confirm rates before transactions; use an official source such as a central bank |
Where Currency Converter fits
Currency Converter is route three: a sidebar converting 180+ currencies at live rates inside Gmail, Docs, Calendar, Slides and Sheets. Sidebar conversions are unlimited and free with no sign-up; a Premium tier adds a Sheets formula with historical rates back to 2000. So the honest advice stands: use the formula where the formula works, and the sidebar where it can't follow.
Sources
- GOOGLEFINANCE – Google Docs Editors Help – read 2026-09-16
- Google Finance disclaimer – read 2026-09-16
- ECB euro foreign exchange reference rates – read 2026-09-16
- Apps Script – Custom functions and Quotas for Google Services – read 2026-09-16
- Currency Converter by 8apps – product claims, read 2026-09-16