The national debt ratio measures the gross debt of federal, state and local governments and social security in relation to GDP.
It provides an indicator for future wellbeing and the state's capacity to act, as these are based on sound finances.
The European Union's Stability and Growth Pact stipulates that Member States should limit their national debt to 60 per cent of economic output.
"Gross" means it only applies to government debt, not asset values. So-called implicit debt is also not included, i.e. the promise of future payments from the state such as pension payments. The total of explicit and implicit debt is known as the "sustainability gap".
The German Federal Bank regularly publishes figures on the national debt ratio.