It isn't possible to give you an answer that would work for your Lab. Every lab is different, and it depends on what you want with your dog. Do you want a working retriever or a show dog? Show judges have different ideas of perfection than field judges. And don't forget, there are different types of Labradors, and there may be difference in the weight of these types. Most vets don't know this, so if your male puppy's father's ideal weight (or your female puppy's mother's ideal weight) is more than average, try to convince your vet that his "standard" doesn't apply to your puppy.    
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At birth, a Labrador puppy from average parents and an average litter (6 puppies) weighs about 1 pound or less. During the first 8 weeks of its life the puppy gains about 2 pounds a week. An 8 week old Labrador puppy weighs between 11 and 17 pounds. From 8 weeks to 26 weeks (6 months) this growth proceeds in about the same way - an average six month old Labrador weighs between 50 and 60 pounds. Dogs are heavier than bitches. After the age of 26 weeks the growth slows down. When your Labrador is one year old, the weight will be 65 to 80 pounds for dogs and 55 to 70 pounds for bitches. Between the age of one year and three years they gain another 5 to 10 pounds.  
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The best way to judge what your Labrador should weigh is to estimate if his weight is appropriate for him. As a Labrador breeder, I like to see some "bone" in my Labradors, and since thrifty feeding during the first six months often is at the expense of the "bone", I like to see some "puppy fat" in my puppies. This puppy fat disappears at adolescence, it serves as a source of energy and it cushions and insulates vital organs.    
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Start just by looking at your puppy from the side. If you don't see any ribs at all, you slightly stroke from front to back over his ribcage and feel for the ribs. If you can feel them with a light touch, your puppy's weight is perfect. If you need more pressure to feel the ribs, he is overweight and it would be better to cut back a little on his food.  
If your puppy is older than six months and you want a healthy working dog, you should be able to see the outline of his last 2 to 3 ribs while he is growing but you shouldn't see more than 5 or 6 ribs. This would be an acceptable weight for a working dog, also when he's an adult. If you can see most of his ribs, you need to feed him more. Sadly enough, the ideal weight for a show dog is 9 to 18 pounds more than the ideal weight for a working dog.    
Judging your Lab's weight this way ensures that it is right for him and not just right for the average member of the breed. It is almost always possible to adjust the feeding schedule to ensure proper weight in a puppy fed primarily dog food. It can be harder if he is getting treats, snacks, or has access to outside food sources like the neighbours. 
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You can use feeding formula and schedules, but it's still better to use the sight and feel method to make sure that your particular puppy is not too fat or too thin.