Convert a hat size
API · /sizes-api
Size Conversion API
healthy
3,233 Subscribers
International size conversion as an API, for the everyday wearables that ship in different scales around the world. The shoe endpoint converts a shoe size between EU (Paris point), UK, US men, US women, Mondopoint and foot length in centimetres — derived from the standard barleycorn and Paris-point relationships — and reports both the exact figure and the nearest standard half-size. The ring endpoint converts a ring size between US numeric, ISO 8653 (inside circumference in millimetres, used across most of Europe), inside diameter, inside circumference and the UK alphabetical scale. The hat endpoint converts a hat size between head circumference (centimetres or inches), the EU metric size, US and UK, with a simple S/M/L band. Everything is computed locally and deterministically, so it is instant and private. Ideal for fashion and footwear e-commerce, jewellery shops, size-guide widgets, returns-reduction tooling and international checkout. Pure local computation — no key, no third-party service, instant. Live, nothing stored. Guidance only — manufacturers' sizing varies, so always check the brand's own chart for a critical fit. 3 endpoints. This is wearable-size conversion; for plain length/weight unit conversion use a unit-conversion API.
api.oanor.com/sizes-api
API health
healthy- Uptime
- 100.00%
- Server probes · 24h
- Avg latency
- 72 ms
- Server probes · 24h
- Subscribers
- 3,233
- active
- Total calls
- 76
- last 7 days
Pricing
Pick a tier — billed monthly, cancel anytime.
Free
Free
- 9,035 calls / month
- 2 requests / second
- Hard cap (429 above quota, no overage)
- 9,035 calls/month
- 2 req/sec
- Shoe + ring + hat
- No credit card
Starter
€10.55 /month
- 18,650 calls / month
- 8 requests / second
- Hard cap (429 above quota, no overage)
- 18.65k calls/month
- 8 req/sec
- EU/UK/US/Mondopoint
- Email support
Pro
€30.45 /month
- 236,500 calls / month
- 20 requests / second
- Hard cap (429 above quota, no overage)
- 236.5k calls/month
- 20 req/sec
- E-commerce / size-guide pipelines
- Priority support
Mega
€68.45 /month
- 1,225,000 calls / month
- 50 requests / second
- Hard cap (429 above quota, no overage)
- 1.225M calls/month
- 50 req/sec
- Platform scale
- Dedicated SLA
Built by
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api.oanor.com/dimweight-api
Frequently asked questions
Quick answers about pricing, quotas, and integration.
How do I get an API key for Size Conversion API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Size Conversion API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Size Conversion API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Size Conversion API cost?
Size Conversion API has a free tier with 100 calls / month. Paid plans start at €10.55 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Size Conversion API GDPR-compliant?
All requests to Size Conversion API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.
Pick an endpoint from the list on the left to see its details and try it.
Code snippets
Sign up to get an API key, then call any path under your slug.
curl https://api.oanor.com/sizes-api/SOME_PATH \
-H "x-oanor-key: oanor_test_..."const res = await fetch("https://api.oanor.com/sizes-api/SOME_PATH", {
headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();$ch = curl_init("https://api.oanor.com/sizes-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);import requests
r = requests.get(
"https://api.oanor.com/sizes-api/SOME_PATH",
headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())Ratings
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