This is a beer mug/stein made by De Porceleyne Fles also known as Royal Delft.
The mug is 4-1/2-in tall and 5-in wide including the handle. The opening diameter is 3-1/8-in and the bottom diameter is 3-5/8-in. The typical Royal Delft mark is on the bottom along with the painter's initials and the date code CJ which stands for 1965 and the model number 1017.
There is crazing, which is not unusual for old pottery.
There is a very tiny chip on the bottom of the mug, which you can see in the picture. Otherwise in excellent condition.
I appreciate and thank you for taking the time to look. Have a wonderful day. .