If you’re looking to either borrow someone else’s MacBook Charger, purchase a replacement or even buy a second one for the office then it pays to be informed on what will and won’t work for your model.
As a general rule, Macbook Pro 15” and 17” models require a 85w adapter, smaller 13” Pros and the older 13” MacBooks take a 60w charger and Air models usually use a 45w charger. Depending on the age of the machine they will use either the newer MagSafe 2 or the older MagSafe standard connection method. The newer 12” MacBooks use a more specific 29w USB-C charger that isn’t compatible with other models.
These are just guidelines and if you want to find the exact model you require you should consult this guide:
Something useful that many people don’t realise is that “you can use a compatible higher wattage adapter without issue, but it won’t make your computer charge faster or operate differently. Lower wattage adapters will not provide enough power”. Meaning that a 85w charger on a 13” MacBook will work fine and do no damage to the machine. If you’re ever considering upgrading to a larger MacBook or want more flexibility to use it between machines then it may be worthwhile looking into the 85w charger to use it with the most amount of Laptops.