When using a single number, it is interpreted as a percentage:
L.pie([50.66, -0.0], 45).addTo(map);
You can also pass an array of {num: Number, label: String}
-maps:
L.pie([50.68, 0.05], [ {num: 45, label: 'Bob'}, {num: 60, label: 'Tom'}, {num: 45, label: 'Ada'} ]).addTo(map);