Flight time: London to Seattle

Route details

Distance breakdown: London to Seattle

The 7,702-km great-circle distance between London (51.47°N, 0.45°W) and Seattle (47.45°N, 122.31°W) spans 4.0° of latitude and 121.9° of longitude, trending primarily west. In miles, this is 4,786 mi or 4159 nautical miles. The great-circle path — the shortest distance over Earth's curved surface — is calculated using the Haversine formula from the two airports' precise coordinates.

Cruise speed and flight phases

On this 7,702-km long-haul route, aircraft spend the majority of the 9h 03m to 10h 14m journey at optimal cruise altitude of 35,000–42,000 feet, where modern wide-body jets achieve true airspeeds of 820–900 km/h (Mach 0.82–0.86). The initial climb and final descent represent a smaller fraction of total flight time compared to shorter routes. Aircraft like the Boeing 777, 787, or Airbus A350 typically operate routes of this distance, with step climbs during the flight to reach progressively more efficient altitudes as fuel burns off and the aircraft lightens.

Ground time and routing overhead

Our 30–50 minutes overhead allowance covers: taxi-out at LHR, takeoff and initial climb, descent and approach at SEA, and taxi-in to the gate. LHR is a major international hub where taxi times of 15–25 minutes are common during peak periods. At SEA, arrival taxi and gate assignment can add 10–20 minutes, especially during busy arrival banks. Oceanic tracks between London and Seattle follow organized route systems (like the North Atlantic Track system) that may add 5–10% to the theoretical great-circle distance. These tracks are assigned daily based on forecast winds.

Return flight: Seattle → London

The return flight from Seattle to London differs noticeably in duration due to upper-atmosphere wind patterns along this oceanic corridor. The jet stream — a high-altitude river of fast-moving air flowing generally from west to east — creates an asymmetry: the eastbound leg (Seattle to London if eastbound, otherwise London to Seattle) is typically 20–60 minutes shorter. Airlines adjust fuel loads and even routing to account for this, sometimes flying more southerly or northerly tracks on the headwind leg to minimize the impact. Over a year, the average time difference between the two directions on this specific route is estimated at 30–45 minutes.

Seasonal variation in flight times

Transatlantic flight times between London and Seattle show clear seasonal patterns driven by the jet stream. In winter (November–March), the jet stream is at its strongest, creating the largest difference between eastbound and westbound times — sometimes exceeding 1 hour. In summer, the jet stream weakens and shifts north, resulting in more symmetrical flight times but potentially more turbulence-related routing deviations. Spring and autumn transitions are the most unpredictable, with the jet stream shifting rapidly. Weather-related delays are more common in winter at both LHR and SEA, which can add to actual gate-to-gate times beyond the cruise-phase effects.

Airport information

Heathrow Airport (LHR) is a major international hub in London, United Kingdom. As a tier-1 airport, it handles high traffic volumes, which means longer average taxi times but also higher flight frequency and competition that can benefit travelers on pricing. Seattle-Tacoma International Airport (SEA) is a major international hub in Seattle, United States. As a tier-1 airport, it handles high traffic volumes, which means longer average taxi times but also higher flight frequency and competition that can benefit travelers on pricing.

Flight times from London to other destinations

Flight time FAQ: London to Seattle