More than 650,000 homes in London are rented in the private market
London Mayor Boris Johnson has launched a new website that reveals the cost of renting homes around the capital.
The London Rents Map shows the average rents for private accommodation for each postcode area in London.
Unlike existing search portals which show asking prices posted by estate agents and individuals, it is based on actual market rents.
Mr Johnson said the service was a "one-stop-shop which will enable tenants and landlords to make sensible choices".
The new website showed the current average rent for a room in a shared house was £92 per week.
More than 650,000 households in London rent their home in the private market, making London's private rented sector by far the largest of any region in England.
Dartford in south east London was the cheapest place to rent in the capital, according to the website, with a two-bedroom home costing an average of just £160 per week.
For a two-bedroom home, the most expensive postcode in terms of average rent was South Kensington, in west London, at £625 a week.
"We know that people looking to rent sometimes don't know where to go for the right information, so this new website is about supporting the market by making that information available," said Mr Johnson.
Tim Eden, from the Valuation Office Agency (VOA), which provides the rental data, said: "Information about the rents private tenants pay, rather than those advertised, is extremely helpful."
Homelessness charity Crisis' private renting manager said The London Rents Map had "the potential to help private sector tenants make informed choices in the market place".