To get from the Eurostar to Gatwick Airport, you can take a combination of the London Underground (tube) and a train or bus. Details for both options are below.
Underground and Train from the Eurostar to Gatwick Airport
From the Eurostar, transfer to the London Underground in St Pancras Station. Take the Victoria line from St Pancras to Victoria Station. The trip will take 9 minutes. Tickets cost £2 if you get an Oyster Card at St Pancras.
From Victoria Station there are trains to Gatwick Airport. You can either take a local train to Gatwick Airport, which takes around 45 minutes, or the Gatwick Express, which takes 30 minutes to get from central London to Gatwick Airport.
Local train tickets to Gatwick Airport from Victoria Station can cost as little as £3.50 for a single if you buy your train ticket online in advance and travel on Southern trains.
Gatwick Express tickets cost £18.90 for a single at the station, but there are discounts available if you buy your Gatwick Express ticket online ahead of time. Online fares start at £16.85 for singles.
Underground and Train from the Eurostar to Gatwick Airport
To take a combination of the tube and a bus to Gatwick Airport, you should first take the tube from St Pancras to either Victoria or West Brompton. National Express run buses from Victoria Coach Station, and easyBus run coaches from near West Brompton.
Getting to Victoria takes 9 minutes, and geting to West Brompton takes 23 minutes. Both journeys cost £2 if you get an Oyster Card at St Pancras.
From Victoria, you can walk to the coach station, which is just down the street. National Express buses take 1 hour and 35 minutes to get to Gatwick, and cost from £5 if you book online in advance.
From West Brompton, you can walk to the easyBus stop on Lillie Road and catch the bus there. It will take approximately 1 hour to get to Gatwick if there is no traffic en route. Tickets cost from £2 if you buy them online ahead of time. You can find additional details about this route here.