Here's how to compare 18 liters (l) and 45 milliliters (ml):

* Understanding Units: Liters (l) and milliliters (ml) are both units of volume.

* Conversion: 1 liter (l) is equal to 1000 milliliters (ml).

* Calculation:

* 18 liters (l) = 18 x 1000 ml = 18000 ml

Conclusion: 18 liters (18000 ml) is much greater than 45 ml.