The viscosity of a fluid describes how easily it flows. Water has a low viscosity, it flows very easily, (it is very runny). Tomato ketchup has a higher viscosity than water, it does not flow very easily, (it seems “thicker” than water). The viscosity of some liquids is shown below.
| Liquid | Viscosity |
| Water | 1 |
| Milk | 3.2 |
| No. 4 fuel oil | 12.6 |
| Cream | 16.5 |
| Vegetable oil | 34.6 |
| SAE 10 oil | 88 |
| Tomato juice | 176 |
| SAE 30 oil | 352 |
| Glycerine | 880 |
| SAE 50 oil | 1561 |
| Honey | 1760 |
| Glue | 3000 |
| Mayonnaise | 5000 |
| Molasses B | 8640 |
| Sour cream | 15,200 |
| SAE 70 oil | 17,640 |
The viscosity of liquids can be compared by timing how long it takes for a known volume of each liquid to flow through a hole.