Fibre Latency Calculator for European Data Centres
Minimum round-trip and one-way delay in optical fibre between 20 European data-centre hubs, from Frankfurt and London to Madrid and Helsinki, with the physics shown.
What is the lowest latency physics allows between Frankfurt and London, or Dublin and Milan? Light in optical fibre covers about 204,000 km per second, so distance alone sets a floor no network can beat. Pick two hubs to see that floor, and adjust the route factor to allow for real cable paths.
Fibre latency between European data-centre hubs
- Light in standard single-mode fibre travels at about 204,107 km/s, so every 1,000 km of fibre adds at least 4.90 ms one way and 9.80 ms to a round trip.
- Among these 20 hubs the shortest straight-line round trip is Amsterdam to Brussels, 1.7 ms; the longest is Helsinki to Lisbon, 32.9 ms.
Minimum round trip between hubs, milliseconds
| From \ to | Amsterdam | Berlin | Brussels | Copenhagen | Dublin | Frankfurt | Helsinki | Lisbon | London | Madrid | Marseille | Milan | Munich | Oslo | Paris | Prague | Stockholm | Vienna | Warsaw | Zurich |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Amsterdam | – | 5.6 | 1.7 | 6.1 | 7.4 | 3.6 | 14.7 | 18.3 | 3.5 | 14.5 | 9.9 | 8.1 | 6.5 | 8.9 | 4.2 | 7.0 | 11.0 | 9.2 | 10.7 | 6.0 |
| Berlin | 5.6 | – | 6.4 | 3.5 | 12.9 | 4.1 | 10.8 | 22.7 | 9.1 | 18.3 | 11.6 | 8.2 | 4.9 | 8.2 | 8.6 | 2.7 | 8.0 | 5.1 | 5.1 | 6.5 |
| Brussels | 1.7 | 6.4 | – | 7.5 | 7.6 | 3.1 | 16.1 | 16.8 | 3.1 | 12.9 | 8.3 | 6.8 | 5.9 | 10.6 | 2.6 | 7.0 | 12.5 | 9.0 | 11.4 | 4.8 |
| Copenhagen | 6.1 | 3.5 | 7.5 | – | 12.1 | 6.6 | 8.7 | 24.3 | 9.4 | 20.3 | 14.4 | 11.4 | 8.2 | 4.7 | 10.1 | 6.2 | 5.1 | 8.5 | 6.6 | 9.4 |
| Dublin | 7.4 | 12.9 | 7.6 | 12.1 | – | 10.7 | 19.8 | 16.1 | 4.5 | 14.2 | 13.8 | 13.9 | 13.5 | 12.4 | 7.7 | 14.3 | 16.0 | 16.5 | 17.9 | 12.1 |
| Frankfurt | 3.6 | 4.1 | 3.1 | 6.6 | 10.7 | – | 14.8 | 18.5 | 6.2 | 14.2 | 7.8 | 5.1 | 3.0 | 10.8 | 4.7 | 4.0 | 11.6 | 5.9 | 8.7 | 3.0 |
| Helsinki | 14.7 | 10.8 | 16.1 | 8.7 | 19.8 | 14.8 | – | 32.9 | 17.8 | 28.9 | 22.4 | 19.0 | 15.6 | 7.7 | 18.7 | 12.8 | 3.9 | 14.1 | 9.0 | 17.4 |
| Lisbon | 18.3 | 22.7 | 16.8 | 24.3 | 16.1 | 18.5 | 32.9 | – | 15.5 | 4.9 | 12.9 | 16.5 | 19.3 | 26.8 | 14.2 | 22.0 | 29.3 | 22.5 | 27.0 | 16.9 |
| London | 3.5 | 9.1 | 3.1 | 9.4 | 4.5 | 6.2 | 17.8 | 15.5 | – | 12.4 | 9.8 | 9.4 | 9.0 | 11.3 | 3.4 | 10.1 | 14.0 | 12.1 | 14.2 | 7.6 |
| Madrid | 14.5 | 18.3 | 12.9 | 20.3 | 14.2 | 14.2 | 28.9 | 4.9 | 12.4 | – | 8.0 | 11.6 | 14.5 | 23.4 | 10.3 | 17.4 | 25.4 | 17.7 | 22.4 | 12.2 |
| Marseille | 9.9 | 11.6 | 8.3 | 14.4 | 13.8 | 7.8 | 22.4 | 12.9 | 9.8 | 8.0 | – | 3.8 | 7.1 | 18.5 | 6.5 | 10.0 | 19.4 | 9.9 | 15.0 | 5.1 |
| Milan | 8.1 | 8.2 | 6.8 | 11.4 | 13.9 | 5.1 | 19.0 | 16.5 | 9.4 | 11.6 | 3.8 | – | 3.4 | 15.8 | 6.3 | 6.3 | 16.2 | 6.1 | 11.2 | 2.1 |
| Munich | 6.5 | 4.9 | 5.9 | 8.2 | 13.5 | 3.0 | 15.6 | 19.3 | 9.0 | 14.5 | 7.1 | 3.4 | – | 12.8 | 6.7 | 2.9 | 12.9 | 3.5 | 7.9 | 2.4 |
| Oslo | 8.9 | 8.2 | 10.6 | 4.7 | 12.4 | 10.8 | 7.7 | 26.8 | 11.3 | 23.4 | 18.5 | 15.8 | 12.8 | – | 13.1 | 10.9 | 4.1 | 13.2 | 10.4 | 13.7 |
| Paris | 4.2 | 8.6 | 2.6 | 10.1 | 7.7 | 4.7 | 18.7 | 14.2 | 3.4 | 10.3 | 6.5 | 6.3 | 6.7 | 13.1 | – | 8.6 | 15.1 | 10.1 | 13.4 | 4.8 |
| Prague | 7.0 | 2.7 | 7.0 | 6.2 | 14.3 | 4.0 | 12.8 | 22.0 | 10.1 | 17.4 | 10.0 | 6.3 | 2.9 | 10.9 | 8.6 | – | 10.3 | 2.5 | 5.1 | 5.2 |
| Stockholm | 11.0 | 8.0 | 12.5 | 5.1 | 16.0 | 11.6 | 3.9 | 29.3 | 14.0 | 25.4 | 19.4 | 16.2 | 12.9 | 4.1 | 15.1 | 10.3 | – | 12.2 | 7.9 | 14.4 |
| Vienna | 9.2 | 5.1 | 9.0 | 8.5 | 16.5 | 5.9 | 14.1 | 22.5 | 12.1 | 17.7 | 9.9 | 6.1 | 3.5 | 13.2 | 10.1 | 2.5 | 12.2 | – | 5.4 | 5.8 |
| Warsaw | 10.7 | 5.1 | 11.4 | 6.6 | 17.9 | 8.7 | 9.0 | 27.0 | 14.2 | 22.4 | 15.0 | 11.2 | 7.9 | 10.4 | 13.4 | 5.1 | 7.9 | 5.4 | – | 10.2 |
| Zurich | 6.0 | 6.5 | 4.8 | 9.4 | 12.1 | 3.0 | 17.4 | 16.9 | 7.6 | 12.2 | 5.1 | 2.1 | 2.4 | 13.7 | 4.8 | 5.2 | 14.4 | 5.8 | 10.2 | – |
Straight-line fibre between city centres, route factor 1. Real routes are longer, so measured round trips are higher.
Round trips along mapped fibre routes, milliseconds
| From \ to | Amsterdam | Berlin | Brussels | Copenhagen | Dublin | Frankfurt | Helsinki | Lisbon | London | Madrid | Marseille | Milan | Munich | Oslo | Paris | Prague | Stockholm | Vienna | Warsaw | Zurich |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Amsterdam | – | 6.4 | 1.8 | 6.8 | – | 3.8 | – | 20.1 | – | 15.7 | 11.4 | 9.2 | 7.2 | 11.6 | 4.4 | 8.1 | 12.4 | 10.8 | 11.9 | 7.0 |
| Berlin | 6.4 | – | 7.1 | 3.9 | – | 4.7 | – | 25.4 | – | 20.9 | 13.4 | 9.5 | 5.4 | 8.8 | 9.7 | 3.1 | 9.5 | 5.9 | 5.6 | 7.7 |
| Brussels | 1.8 | 7.1 | – | 8.5 | – | 3.5 | – | 18.5 | – | 14.1 | 9.8 | 8.9 | 6.8 | 13.4 | 2.8 | 7.8 | 14.1 | 10.5 | 12.4 | 6.7 |
| Copenhagen | 6.8 | 3.9 | 8.5 | – | – | 7.1 | – | 26.8 | – | 22.4 | 15.8 | 12.7 | 9.2 | 4.9 | 11.1 | 7.0 | 5.6 | 9.7 | 8.9 | 10.5 |
| Dublin | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| Frankfurt | 3.8 | 4.7 | 3.5 | 7.1 | – | – | – | 21.2 | – | 16.8 | 8.8 | 5.6 | 3.3 | 11.9 | 5.9 | 4.4 | 12.7 | 7.0 | 9.5 | 3.4 |
| Helsinki | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| Lisbon | 20.1 | 25.4 | 18.5 | 26.8 | – | 21.2 | – | – | – | 5.2 | 15.5 | 19.7 | 21.8 | 31.7 | 15.7 | 24.6 | 32.4 | 25.0 | 30.7 | 18.8 |
| London | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| Madrid | 15.7 | 20.9 | 14.1 | 22.4 | – | 16.8 | – | 5.2 | – | – | 10.3 | 14.5 | 17.3 | 27.3 | 11.3 | 20.1 | 28.0 | 20.6 | 26.2 | 14.3 |
| Marseille | 11.4 | 13.4 | 9.8 | 15.8 | – | 8.8 | – | 15.5 | – | 10.3 | – | 4.3 | 8.4 | 20.7 | 7.0 | 11.8 | 21.4 | 11.0 | 17.4 | 6.3 |
| Milan | 9.2 | 9.5 | 8.9 | 12.7 | – | 5.6 | – | 19.7 | – | 14.5 | 4.3 | – | 4.1 | 17.5 | 8.0 | 7.5 | 18.3 | 6.7 | 13.1 | 2.2 |
| Munich | 7.2 | 5.4 | 6.8 | 9.2 | – | 3.3 | – | 21.8 | – | 17.3 | 8.4 | 4.1 | – | 14.1 | 7.0 | 3.5 | 14.8 | 3.8 | 10.0 | 3.0 |
| Oslo | 11.6 | 8.8 | 13.4 | 4.9 | – | 11.9 | – | 31.7 | – | 27.3 | 20.7 | 17.5 | 14.1 | – | 16.0 | 11.9 | 4.3 | 14.6 | 13.8 | 15.3 |
| Paris | 4.4 | 9.7 | 2.8 | 11.1 | – | 5.9 | – | 15.7 | – | 11.3 | 7.0 | 8.0 | 7.0 | 16.0 | – | 9.2 | 16.7 | 10.8 | 15.1 | 5.9 |
| Prague | 8.1 | 3.1 | 7.8 | 7.0 | – | 4.4 | – | 24.6 | – | 20.1 | 11.8 | 7.5 | 3.5 | 11.9 | 9.2 | – | 12.6 | 2.8 | 6.7 | 6.1 |
| Stockholm | 12.4 | 9.5 | 14.1 | 5.6 | – | 12.7 | – | 32.4 | – | 28.0 | 21.4 | 18.3 | 14.8 | 4.3 | 16.7 | 12.6 | – | 15.3 | – | 16.1 |
| Vienna | 10.8 | 5.9 | 10.5 | 9.7 | – | 7.0 | – | 25.0 | – | 20.6 | 11.0 | 6.7 | 3.8 | 14.6 | 10.8 | 2.8 | 15.3 | – | 6.4 | 6.2 |
| Warsaw | 11.9 | 5.6 | 12.4 | 8.9 | – | 9.5 | – | 30.7 | – | 26.2 | 17.4 | 13.1 | 10.0 | 13.8 | 15.1 | 6.7 | – | 6.4 | – | 12.2 |
| Zurich | 7.0 | 7.7 | 6.7 | 10.5 | – | 3.4 | – | 18.8 | – | 14.3 | 6.3 | 2.2 | 3.0 | 15.3 | 5.9 | 6.1 | 16.1 | 6.2 | 12.2 | – |
Shortest route along operational fibre on the ITU Transmission Networks map, 135 of 190 pairs. A dash means the map cannot route the pair over land: London and Dublin have no mapped land link (37 pairs), and Helsinki and some Baltic pairs are linked only round a sea (18 pairs). Real traffic there uses submarine cables, which this map does not include.
Method and sources
Distance is the great-circle distance between city centres (haversine formula on a sphere of radius 6,371.0088 km, the IUGG mean Earth radius). The fibre path is that distance times the route factor you set. Delay is path length × ng / c, with group index ng = 1.4688 at 1550 nm for G.652.D single-mode fibre (FiberHome, Low Water Peak Single-Mode Optical Fiber (G.652.D) specifications) and c = 299,792.458 km/s (SI).
This is a physical lower bound. It leaves out the extra length of real cable routes, amplifiers, switching, serialisation and queueing, all of which add delay. City coordinates come from Wikidata (CC0), retrieved 2026-10-10; distances are between city centres, not specific facilities.
Mapped routes: the shortest path along operational fibre on the International Telecommunication Union’s Transmission Networks map (BBmaps, retrieved 2026-09-19), shown by permission of the ITU. Only route lengths are published. The map traces backbone corridors at about 3 km resolution, so it straightens bends and real routes are usually longer: mapped figures are a tighter lower bound, not a measurement.