What is the difference?

The weighted GPA takes into account the difficulty of your coursework like weighted classes such as Honors English, AP BIO and IB Maths etc. If you take difficult classes the weighted GPA reflects the course rigor on your transcript. The standard unweighted GPA does not.

An unweighted GPA on a 4.0 scale means the max GPA is based on

A=4.0, A-=3.7, B+=3.3, B=3.0, B-=2.7, C+=2.3, C=2.0 etc.

A weighted GPA on 4.0 scale means that

A=4.0, A-=3.7, B+=3.3, B=3.0, B-=2.7, C+=2.3, C=2.0, etc. but you give yourself a boost of say 1.0 for an AP class and say 0.50 for an honors class and some schools give a 2.0 boost for an IB class. (keep in mind each and every school treats weighed classes differently)

This means if you get an A in IP Math you would count that as a 6.0, not a 4.0

If you get an A in AP Calculus you would count this as a 5.0, not a 4.0

And if you get an A in Geometry honors you would count this as a 4.5, not a 4.0

So for most circumstances, the max unweighted GPA is a 4.0 out of 4.0 but a weighted GPA with the same grades can be between 4.0-6.0 (if you took all IB classes and got all As)

So while Cameron’s answer is fairly good there is a lot of nuance and there really is no standerized scale. At my school honors isn’t weighted and all As are 4.0 all Bs are 3.0 etc.

The typical formula used for weighted is x unweighted GPA + 1 for IB and AP classes. While my school doesn’t do it honors typically gets a .5 boost.

So if you only got Bs in all AP IB courses you’d have a 4.0 GPA despite having a 3.0 UW GPA.

Hope this helps and please comment if you need clarification as I’d be happy to help clarify!