how i manually find resolution if i know the mode i used

for example

i used text mode (03h) having 80x25 then how i calculated the resolution

(i.e 720*400)

any idea how (720*400) comes i.e any formula

for example

i used text mode (03h) having 80x25 then how i calculated the resolution

(i.e 720*400)

any idea how (720*400) comes i.e any formula

You need to know the size of a single character... unfortunately, this is not a constant - it differs. So, no, there is no formula. A complete list of resolutions is here:

http://www.ctyme.com/intr/rb-0069.htm

Ossa

http://www.ctyme.com/intr/rb-0069.htm

Ossa