I purchased a Heflinger mare to breed this spring with a Jack , the colt will be at full growth about 14 hands , I live next to a fram pasture and want to rent land from farmer for mule to graze on and make shelter Question is how much land do I need to rent for mother horse and baby mule ? I will seed this land so there is lots of green for them !

Your question is hard to answer w/o knowing the growing conditions. Typical of grazers, they love eating new growth (walking right over lusher pastures). Best way to control this is to have crossfences, allowing one portion to rest, while grazing the other.
Long term, mules are very easy keepers, with little need for any supplemental feeding (other than decent hay). Sure, they'll eat the sweet feed, but typically it's not needed.
Short term: Extra feed/supplements will be required for the mare, then the mule for 4-5 yrs, too ensure body mass and good muscle.
Then you'll only have 30 yrs or so of a hay/grass `eatin longear.

To get an approximate answer to your question, here it is. Decent conditions, 6 acres will do nicely. Add 2 acres for an additional animal. I pasture ten, and in a wet year I can get all ten through on 20 acres, till the snow and freeze do us in. I have no thin animals. This is in Iowa.

Generally 1-2 acres of good grass per animal, when you have grass. In N. FL we have grass @ 8 months a year. I run 3 mules on 6 acres of pasture, but I only let them graze @ 6 hrs a day. Be careful in the spring as the lush new grass can cause founder. Let them graze briefly & extend it a little at a time.

Thank You gentlemen for you information !

All areas are different and no one can answer that question except the locals to that area, that is where to direct your question, ask your local County agent he can tell you..

Our ranch in far west Texas would take over a hundred acres to run one horse on a good year. My place in Idaho will run 3 horses on 3 or 4 acres year around because its planted grasses and irragated pasture.....

Both ranches have their good and bad points but one is about as good as the other.