Is there a free currency converter API?

Yes. You can make an anonymous evaluation request without a key. A free account includes 5,000 calls per month at 10 requests per minute, with no card required.

Can the API convert several currencies at once?

Yes. POST /v1/convert accepts a source currency and a list of target-currency and amount pairs. Each conversion counts toward quota separately.

Are the converted amounts suitable for settlement?

No. The rates are indicative and intended for estimates, display, reporting, and analytics. Use the institution executing the payment or trade for a settlement quote.

Currency Converter API for Developers

Convert one amount or a batch of amounts with JSON, source and observation fields, and no API key for the first request.

exchangerate.devSep 20, 20267 min read

A useful currency converter API gives you more than a multiplied number. It shows the rate, converted amount, source, observation time, market session, and whether the pair was derived. exchangerate.dev includes that context in every conversion response.

Key points

Try GET /v1/convert/USD/EUR/100 without a key; use a server-side key for production.

Single and batch conversion endpoints return rate provenance and freshness metadata.

Converted amounts are quantized for the target currency; keep the rate at full precision.

Rates are indicative estimates, not executable bank, card, or settlement quotes.

Make your first currency conversion request

The path contains the source currency, target currency, and amount. This request is enough to try the API and inspect the response. For a deployed application, create a free key and keep it on your server.

curl · convert 100 USD to EUR

curl "https://api.exchangerate.dev/v1/convert/USD/EUR/100"

The response includes from, to, amount, rate, converted, derived, and derivation_bps_max, plus the normal response envelope: source, sources, market_session, timestamp, and data_updated_at. Those fields let the application explain what it converted and how fresh the underlying observation was.

Convert several amounts in one request

Use the POST endpoint when a job needs several target currencies. Each pair counts toward quota separately, but batching reduces network round trips and keeps the results in one response.

curl · batch conversion

curl -X POST "https://api.exchangerate.dev/v1/convert" \
  -H "Authorization: Bearer $EXCHANGERATE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"from":"USD","pairs":[["EUR",100],["GBP",50],["JPY",1000]]}'

Keep rates precise and round money at the boundary

Store the returned rate at full precision. Round the final money amount according to the target currency and the rules of your product. The conversion endpoint quantizes converted for the target currency, but accounting systems should still preserve the original amount, rate, currency codes, and observation time beside the booked result.

Indicative is not executable

A currency API estimates value. A bank, card network, broker, or payment processor supplies the executable quote that actually settles a transaction, including its spread and fees.

Cache by data cadence, not page views

Do not call the upstream API once per browser render. Fetch on the server, cache a successful response, and reuse it until your product needs a refresh. Preserve data_updated_at when a refresh fails so users can see the age of the last good observation.

Set a request timeout and handle 429 and 503 explicitly.
Keep the API key in a server environment variable, never in browser JavaScript.
Retain the last successful response for a bounded fallback window.
Display the observation time and rate class when freshness matters.

Use the pattern in your stack

Follow the focused guides for React, Ruby on Rails, Shopify, or WooCommerce. Each keeps the upstream call on the server and separates display estimates from executable checkout prices.

Choose the endpoint that matches the job

JobEndpointWhy

Convert one amountGET /v1/convert/{from}/{to}/{amount}One rate and converted amount

Convert a basketPOST /v1/convertSeveral conversions in one response

Display a quote onlyGET /v1/rate/{pair}Flat pair response without an amount

Build a historical seriesGET /v1/rangeDaily observations across a date window

Need to check a past rate before writing code? Use the historical exchange-rate lookup, then copy the matching API request.

exchangerate.dev

Practical integration guides for developers working with currency data.