Of the total area that is used by humans (Agriculture, Urban and Built-up Land),
- urban and built-up land is 1m km²,
- agriculture is 48m km²,
so agriculture is 48 of 49 millions km² used, that’s 98%. The remaining 2% are all streets and housing and other infrastructure together.
Because they are habitable? You can build on them, or use boats and such to live on them.
But if we count boats, then a large part of the oceans should count as habitable as well.