0.5 Liters is greater than 400 milliliters.
In a liter, there are 1000 milliliters. That being said, you can do 1 of 2 things:
1. Multiply 0.5 by 1000 to show how many milliliters there are (500). 500ML is greater than 400ML. OR
2. Divide 400 by 1000 to show how much of a liter there is (0.4). 0.5L is greater than 0.4L.
Thus meaning 0.5 Liters is greater. I hope this helps!