Seattle, USA to London, UK: ICMP round-trip time measurements with packet loss, jitter, and route efficiency data from the latest test round.

🇺🇸 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
Destination Region	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.

Ping series: SEA → LON

50 ICMP echo samples at 100 ms intervals · round 2026-08-16T04:07:28Z · avg 124.1 ± 0.56 ms (SE)

Sample distribution: box = interquartile range (120.8–126.3 ms), median 123.3 ms · whiskers = min–max · diamond = round average · each dot is one measured sample.

How to read this chart

The shaded band spans the measured minimum to maximum RTT of all samples collected up to that point, and the thin line traces the running average. The final position therefore matches the round statistics exactly — the band only widens when a new extreme sample arrives.

The dashed line is the round average, and the shaded band at the bottom is the theoretical fiber-optic floor (75.6 ms) for this route.

Full 50-sample dataset

Seq	Offset (ms)	RTT (ms)
1	0	123.76
2	100	120.14
3	200	128.20
4	300	128.29
5	400	124.56
6	500	123.77
7	600	120.18
8	700	122.38
9	800	123.37
10	900	120.54
11	1000	118.94
12	1100	137.20
13	1200	127.22
14	1300	126.40
15	1400	126.70
16	1500	133.59
17	1600	126.17
18	1700	126.92
19	1800	122.51
20	1900	119.93
21	2000	125.95
22	2100	122.21
23	2200	123.45
24	2300	133.61
25	2400	126.22
26	2500	120.86
27	2600	121.07
28	2700	120.15
29	2800	120.26
30	2900	125.95
31	3000	121.19
32	3100	119.59
33	3200	121.78
34	3300	120.75
35	3400	123.14
36	3500	129.76
37	3600	123.04
38	3700	119.98
39	3800	120.61
40	3900	119.47
41	4000	122.04
42	4100	120.08
43	4200	126.36
44	4300	124.91
45	4400	124.42
46	4500	126.23
47	4600	126.76
48	4700	122.36
49	4800	129.55
50	4900	122.48

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 for citation guidance.

Download this dataset

Per-route ICMP ping series, released under CC BY 4.0. Uncompressed plain text — no decompression step needed.

CSV JSON YAML Full dataset

Theoretical Fiber Latency

The public physical reference uses the GeoNames city centres for Seattle (47.60621, -122.33207) and London (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.

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%

RTT trend

Estimated route stability across the selected time window.

Average: 124.2 ms
Minimum: 123.0 ms
Maximum: 125.5 ms
Average loss: 0.01%

Route Context

Departure PoP: Seattle (SEA)
Destination PoP: London (LON)
Region overview: North America → Europe
Full global matrix: Backbone Latency Matrix
Physical methodology: Theoretical Fiber Latency

Reverse direction

London to Seattle latency and RTT — 123.2 ms

Fastest routes departing Seattle (SEA)

Seattle to Los Angeles latency and RTT — 25.9 ms
Seattle to New York latency and RTT — 59.5 ms
Seattle to Ashburn latency and RTT — 61.5 ms
Seattle to Miami latency and RTT — 81.7 ms
Seattle to Tokyo latency and RTT — 85 ms

Fastest routes arriving at London (LON)

Amsterdam to London latency and RTT — 5.2 ms
Paris to London latency and RTT — 6.4 ms
Frankfurt to London latency and RTT — 12.9 ms
Berlin to London latency and RTT — 15.2 ms
Marseille to London latency and RTT — 18.9 ms

Same corridor (North America → Europe)

New York to London latency and RTT — 63.5 ms
New York to Amsterdam latency and RTT — 68.7 ms
New York to Paris latency and 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. 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 or browse more city-pair routes.

Seattle, USA → London, UK RTT