# Seattle, USA → London, UK RTT

🇺🇸 **Seattle, USA (SEA)** → 🇬🇧 **London, UK (LON)**

Measurement round: `2026-08-16T04:07:28Z`.

For the 2026-08-16T04:07:28Z round, the Seattle-to-London ICMP echo test averaged 124.1 ms, with a narrow observed range from 118.94 ms to 137.2 ms and a standard deviation of 3.96 ms. All 50 packets returned successfully, earning a 'Good' latency tier.

The geodesic between Seattle and London is about 7,722.7 km, and the estimated fiber floor for that distance is around 75.6 ms. The measured average is 1.64 times that floor, equivalent to 60.9% fiber efficiency, which indicates a solidly efficient transatlantic route.

Within the 19 outbound routes measured from Seattle, this path ranked 7th in average round-trip time. The observed variation of about 3.2% of the average sits just below the 3.28% median for the route set, and with 3.75 ms jitter and zero loss, the route delivered consistent transatlantic timing.

## Latency Summary

| Metric               | Value                                                        |
| -------------------- | ------------------------------------------------------------ |
| RTT                  | **124.1 ms**                                                 |
| Jitter               | **3.75 ms**                                                  |
| Packet Loss          | **0%**                                                       |
| Standard Fiber Floor | **75.63 ms**                                                 |
| Fiber Efficiency     | **60.9%**                                                    |
| Latency Tier         | Good                                                         |
| Source Region        | [North America](/docs/network/latency/regions/north-america) |
| Destination Region   | [Europe](/docs/network/latency/regions/europe)               |

## Ping Measurement Series

The chart below renders the 50-sample ICMP echo measurement round for this route; an accessible table of every sample is included with the chart.

## Download This Route's Data

This route's measurement round is published as open data (CC BY 4.0) in CSV, JSON, and YAML. See [About This Measurement](#about-this-measurement) for citation guidance.

## Theoretical Fiber Latency

The public physical reference uses the GeoNames city centres for [Seattle](https://www.geonames.org/5809844) (47.60621, -122.33207) and [London](https://www.geonames.org/2643743) (51.50853, -0.12574). It does not disclose either facility address.

| Physical Reference                            | Value          |
| --------------------------------------------- | -------------- |
| WGS-84 geodesic distance                      | **7,722.7 km** |
| Vacuum RTT floor                              | **51.52 ms**   |
| Standard fiber RTT floor ($n_g=1.4679$)       | **75.63 ms**   |
| Low-latency fiber material floor              | **75.32 ms**   |
| Engineering floor (5% path allowance)         | **79.42 ms**   |
| Research 1.33× mapped-fiber reference         | **100.58 ms**  |
| Estimated unamplified path loss               | **1621.8 dB**  |
| Transparent optical spans / inline amplifiers | **102 / 101**  |
| Published RTT inflation over fiber floor      | **1.64×**      |

Attenuation is used to estimate the number of 80 km optical spans; it does not directly slow light. See the full [theoretical fiber latency, GeoNames, attenuation, and amplifier methodology](/docs/network/latency/theoretical-fiber-latency).

## Stability & Trend

The current measurement round (2026-08-16T04:07:28Z) collected 50 ICMP echo samples on this route. Distribution statistics from that round:

| Round Statistic    | Value         |
| ------------------ | ------------- |
| Minimum RTT        | **118.94 ms** |
| Average RTT        | **124.1 ms**  |
| Maximum RTT        | **137.2 ms**  |
| Standard deviation | **3.96 ms**   |
| Stdev / average    | **3.2%**      |

## Route Context

* Departure PoP: [Seattle (SEA)](/docs/network/latency/sea-seattle)
* Destination PoP: [London (LON)](/docs/network/latency/lon-london)
* Region overview: [North America](/docs/network/latency/regions/north-america) → [Europe](/docs/network/latency/regions/europe)
* Full global matrix: [Backbone Latency Matrix](/docs/network/latency)
* Physical methodology: [Theoretical Fiber Latency](/docs/network/latency/theoretical-fiber-latency)

## Related City-Pair Routes

**Reverse direction**

* [London to Seattle latency and RTT](/docs/network/latency/pairs/lon-sea-rtt) — 123.2 ms

**Fastest routes departing Seattle (SEA)**

* [Seattle to Los Angeles latency and RTT](/docs/network/latency/pairs/sea-lax-rtt) — 25.9 ms
* [Seattle to New York latency and RTT](/docs/network/latency/pairs/sea-nyc-rtt) — 59.5 ms
* [Seattle to Ashburn latency and RTT](/docs/network/latency/pairs/sea-iad-rtt) — 61.5 ms
* [Seattle to Miami latency and RTT](/docs/network/latency/pairs/sea-mia-rtt) — 81.7 ms
* [Seattle to Tokyo latency and RTT](/docs/network/latency/pairs/sea-tyo-rtt) — 85 ms

**Fastest routes arriving at London (LON)**

* [Amsterdam to London latency and RTT](/docs/network/latency/pairs/ams-lon-rtt) — 5.2 ms
* [Paris to London latency and RTT](/docs/network/latency/pairs/par-lon-rtt) — 6.4 ms
* [Frankfurt to London latency and RTT](/docs/network/latency/pairs/fra-lon-rtt) — 12.9 ms
* [Berlin to London latency and RTT](/docs/network/latency/pairs/ber-lon-rtt) — 15.2 ms
* [Marseille to London latency and RTT](/docs/network/latency/pairs/mrs-lon-rtt) — 18.9 ms

**Same corridor (North America → Europe)**

* [New York to London latency and RTT](/docs/network/latency/pairs/nyc-lon-rtt) — 63.5 ms
* [New York to Amsterdam latency and RTT](/docs/network/latency/pairs/nyc-ams-rtt) — 68.7 ms
* [New York to Paris latency and RTT](/docs/network/latency/pairs/nyc-par-rtt) — 68.9 ms

## About This Measurement

Published RTT reflects best-case backbone path behavior measured with ICMP echo probes between PoPs. End-user latency also depends on local access networks, congestion, routing policy, and traffic engineering. None of these values is an SLA.

The measurement round behind this page is published as open data under **CC BY 4.0** in the [Hats Network latency dataset](/opendata/latency/). Per-pair files are available at `/opendata/latency/latest/pairs/sea-lon.pings.{csv,json,yaml}`. When citing, include the route, the measurement round timestamp, and the dataset version — for example: "Hats Network latency dataset, Seattle → London round 2026-08-16T04:07:28Z, CC BY 4.0".

***

*Data auto-generated on August 16, 2026. Explore the [full interactive latency matrix](/docs/network/latency) or browse more [city-pair routes](/docs/network/latency/pairs).*

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## License and attribution

- **Canonical source:** [View the human-readable HTML page](https://hatsnet.io/docs/network/latency/pairs/sea-lon-rtt).
- **Original documentation:** © Hats Network Inc., licensed under [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/).
- **Public latency data:** © Hats Network Inc., licensed under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/).
- **Full terms:** [Content and Data License](https://hatsnet.io/docs/legal/content-and-data-license) — includes attribution requirements, third-party material, trademarks, source code and other exclusions.