The transparent calculation
RTT = 2 × 5,570 km ÷ 204,000 km/s × 1,000, which is approximately 54.6 ms.
PHYSICS EXPLAINER
New York to London Ping: Minimum RTT Explained
New York and London are about 5,570 km apart. Even a perfect 5,570 km fiber path has a propagation-only RTT near 54.6 ms at 204,000 km/s; a real cable and terrestrial route is longer and adds network overhead.
Editorial model reviewed · Internet Analysis Editorial Team
Why observed results vary
Endpoints may be outside each city center, traffic may use different subsea cables, and peering or congestion can change the route and delay.
New York–London RTT: compare the assumptions
The geographic model uses approximately 5,570 km between city-centre reference points. The table assumes equal modeled distance in both directions and excludes access links, equipment, queueing and endpoint processing. It is not a survey of submarine cables or measured pings.
| Scenario | One-way modeled path | Propagation-only RTT |
|---|---|---|
| Vacuum-speed geographic reference | 5,570 km | 37.2 ms |
| Fiber, geographic reference | 5,570 km | 54.6 ms |
| Fiber, 20% longer assumed route | 6,684 km | 65.5 ms |
| Fiber, 40% longer assumed route | 7,798 km | 76.5 ms |
Why a website may appear to respond in 5 ms
A London-branded website can be served by a nearby CDN edge or proxy. A tool may use a different server, show a placeholder or time work that is not a complete round trip. Verify the responding IP, endpoint location and method before calling a result transatlantic RTT.
How to make a useful comparison
- Choose endpoints actually located in New York and London. A city name in a URL is not enough.
- Record protocol, date, successful samples and repeatable destination.
- Compare repeated idle measurements. Route information helps, but individual hop geolocation can be wrong.
- Keep measured RTT separate from the geographic model. Unknown cable length prevents exact overhead attribution.
Understand zero-ping readings and fiber delay per kilometre. Our browser timing tool measures its own destination, not automatically this transatlantic route.
QUESTIONS
Common questions
Could a radio or vacuum route be faster?
Its propagation speed could be faster than fiber, but it would still need a feasible physical route and network infrastructure.
Is 55 ms guaranteed?
No. It is an idealized floor based on straight-line distance, not a predicted real-world RTT.
Why might a tool show 5 ms for a London website from New York?
A CDN, proxy or different test endpoint may answer nearby. Verify the server that actually answered and the timing method before treating the result as a New York–London RTT.
Formula and limitations
Values use transparent approximations described in the article.
Reference constants: NIST speed of light in vacuum. Fiber propagation uses a disclosed engineering approximation of 204,000 km/s; actual group velocity varies with the fiber.