The most accurate way to determine a cat's temperature is by taking their temperature with a rectal thermometer.
Here are some tips on what to look for when buying a thermometer for your cat.
When choosing a thermometer, you can buy a human type one at your local drug store. Choose a model that is fast (reads in 5 - 10 seconds) and has a flexible soft tip.
The softer tip is more comfortable for your cat. They generally run around $5.00 to $7.00. Label it for your cat and keep it with your pet first aid supplies.