That's a pretty good way to guess, Serena, but if it's a heavier boned, larger breed dog remember it's not going to reach full physical size until it's about a year and a half old. I've noticed that double the weight at the four month stage, plus 15 to 20 percent of the doubled weight is gives you a pretty good guesstimate.
I've learned that little formula by the hands on method . . . or should I say, "paws on" . . . shoulders, much to my chagrin! (lol) Of course, it may have something to do with getting proper nutrition and the excessive amount of exercise my bunch gets, too.
One thing's for sure, a Rottie/Blue Heeler cross should have a very interesting personality and have the potential to be impressively bright.
I've learned that little formula by the hands on method . . . or should I say, "paws on" . . . shoulders, much to my chagrin! (lol) Of course, it may have something to do with getting proper nutrition and the excessive amount of exercise my bunch gets, too.
One thing's for sure, a Rottie/Blue Heeler cross should have a very interesting personality and have the potential to be impressively bright.
It kind of depends on which side of its genetics your dog inherited his size from. Blue heelers usually don't top 45lbs. But, he's obviously going to be bigger than that... A sign that's always been pretty good for me is to look at the thickness of the legs & the size of the paws. If they still look abnormally large at 6-8 months, your dog probably isn't done growing.
YIKES...if you go by paw size.............Hammie will be a big boy. He has the biggest paws and ears I've ever seen. Think it'll take him two years to grow into them???? I've looked at his paws so many times and wondered if they weren't 'swollen'...........my hubby just laughs. They are as big as a child's hands........a big child. I know, I wash them everyday before he comes in. So, if a dog is 50 lbs. at 4 mos............it is to assume they will be around 100 lbs at full growth??? I hope not. soooooo........tell me that isn't so. 
Entirely possible, Debi, but take a good look at the bone structure and adjust the estimate by how heavy it looks and if it's geared to a dog of that size. A great deal of a dog's weight will be in the skeleton. When it comes down to it, though, they end up being the size they end up being.
About the ears; Bimmer's ears still look oversized. You can see it in his close up photos. They don't necessarily grow into the ears. Bimmer's a throwback to the fairy tale; "the better to hear you with, my dear."
About the ears; Bimmer's ears still look oversized. You can see it in his close up photos. They don't necessarily grow into the ears. Bimmer's a throwback to the fairy tale; "the better to hear you with, my dear."