For the first time, the United Nations' appeal includes funding for life-saving food, shelter and other humanitarian aid as well as development support, as the bloody war in Syria heads towards a fifth year.
UN agencies said at its launch in Berlin that $2.9 billion (2.4 billion euros) was needed to help 12.2 million people inside Syria in 2015.
A further $5.5 billion is eyed for Syrians who have sought refuge in neighbouring countries and more than a million people in host communities, it said.
The Berlin appeal for Syria is slightly higher than an indicative amount announced in Geneva earlier this month, which did not include funding needs of neighbouring countries.
The UN is planning for up to 4.3 million refugees in countries neighbouring Syria by the end of 2015, it added.
"For those that think that this is a lot of money, I don't remember any bailout of any medium-sized bank that has cost less than this," UN High Commissioner for Refugees Antonio Guterres told reporters.
He warned that refugees and people displaced inside Syria had exhausted their savings and that host countries were at "breaking point".
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United Nations humanitarian chief Valerie Amos said Syria had slumped from a middle income country to struggling with widespread poverty.
"People affected by conflict need food, shelter, water, medicine and protection. But they also need support in rebuilding their livelihoods, maintaining education and health services and rebuilding fragmented communities.
"The conflict in Syria is not only destroying people's lives today but will continue to erode their capacity to cope far into the future if we don't take a more holistic approach now," Amos, UN under-secretary general for humanitarian affairs, said.
Germany hosted an international conference on the Syrian refugee crisis in October which vowed to extend long-term financial aid to countries such as Lebanon and Jordan struggling under the influx of millions of Syrian refugees.
"The humanitarian crisis in Syria and the neighbouring countries poses a threat to the stability of the whole region," Foreign Minister Frank-Walter Steinmeier said Thursday.
"This is a call to the solidarity of all nations, and my country is willing to do its part," he added.
More than 200,000 people have been killed in the Syria conflict, which erupted in March 2011.