This is a link to a growth chart for Goldendoodles. I don't know if it is applicable to Labradoodles but, it may be pretty close. The rule of thumb is to double the weight at four months and add up to 10 pounds.
Either using the growth chart or the rule of thumb estimation - it appears that my Holly, who was about 35 pounds at 4 months and is close to 50 pounds at 6-month will be well over 70 pounds at full growth.
This is hard to believe of the little puppy who was 7 3/4 pounds at seven weeks when I got her from Cheyenne valley Labradoodles and Goldendoodles, north of Dallas, TX.
Heather Goines picked Holly out of the litter for us. I was a little apprehensive having a breeder pick my dog but, Heather did a wonderful job. We could not imagine a better, smarter or more loving Doodle than our Holly.
Here is Holly at 7 weeks and 7 3/4 pounds and Holly at 6 months and just under 50 pounds. What a change! She is now an adolescent.