NAIROBI (Reuters) - Kenya's gross domestic product (GDP) was estimated to be 25 percent bigger after the authorities changed the base calculation year to 2009 from 2001, sending the east African nation into the top 10 of Africa's largest economies. Economic output was calculated to be 4.76 trillion shillings ($53.3 billion) in 2013 after rebasing, up from 3.8 trillion shillings ($42.6 billion), the minister for devolution and planning, Anne Waiguru, told a news conference on Tuesday. Growth in 2013 was calculated to have been 5.7 percent after rebasing, up from the previous estimate of 4.7 percent. The rebasing exercise means debt levels fall as a proportion of GDP, a closely watched ratio. This could give the government some leeway for more borrowing to help finance its plans to build new transport links and repair creaking infrastructure. But revising the estimated size of GDP does not change Kenya's ability to repay additional loans nor does it mean it has more income to spend on development in a nation where many live in villages connected by dirt roads and without power. "Debt service capacity and export growth, neither of which are expected to be substantially revised, are much more important when it comes to being able to take on more debt," Razia Khan, Africa economist at Standard Chartered Bank, said ahead of Tuesday's announcement. Kenya's move follows the far more dramatic rebasing earlier this year of Nigeria's economy. It changed the base year from 1990 to 2010 and, as a result, vaulted above South Africa to become Africa's biggest economy. Kenya's rebasing was less pronounced because the gap with 2001 and the new base year of 2009 was much shorter. But it still meant Kenya rises from 12th to 9th, above Ghana, in Africa's GDP rankings, based on a World Bank table for 2013. (1 US dollar = 89.2500 Kenyan shilling)