When you're shopping for a 50 lb dog, you're in a sweet spot. Not a small breed, not a giant breed. Just a solid medium-to-large dog. The feeding chart from PetMD puts a 36-50 pound adult at roughly 2⅓ to 3 cups of dry food a day, depending on the calorie density of the food. That's manageable. A 30 lb bag lasts you about a month if you're not spilling it all over the garage floor like I do. I've had good luck with the standard Purina Pro Plan formulas. The Chicken and Rice Shredded Blend is 379 calories per cup, which lands right in the middle of that range. Blue Buffalo Life Protection is another one I've used, though some dogs get gassy on it. Your mileage may vary.
For the 100 lb dog, everything scales up. A 76-100 pound dog needs 3¾ to 4⅔ cups per day according to that same chart, and once you cross the 100-pound mark you add another quarter cup for every extra 10 pounds. That's a lot of kibble. You burn through a 50 lb bag in a hurry. My big shepherd went through a phase where I swear he was eating more than my grocery budget. I tried a few grain-free options from the Chewy bestseller list, like Taste of the Wild, but after a while I came back to Diamond Naturals. The Lamb Meal and Rice formula comes in a 50 lb bag and it's a solid mid-range food, with probiotics and decent protein. The ingredients won't make you cry tears of joy but they're not junk either.
Now let's talk about that 50 lb bag specifically. If you've got a large dog or even two medium dogs, buying in bulk is the only way to not go broke. Amazon's results page for "dog food 50 lb bag" is basically a list of the usual suspects: Diamond, Purina, Pedigree, sometimes Victor. The AKC notes that dry food is the most common choice for large breeds because it's convenient and often the least expensive option. No surprises there. Wet food for a 100 lb dog would require a second mortgage. I've fed Diamond Naturals in the 50 lb format and it holds up fine in storage if you keep it in a sealed bin. The kibble size is on the larger side, which my shepherd crunches through fine but my friend's 45-pound collie mix had to work at it a bit.
You also asked about a 50 kg dog, which is about 110 pounds. That's firmly in the giant breed territory. For those dogs, the AKC emphasizes looking for a large or giant breed formula that controls calcium and phosphorus to protect developing joints if your dog is still young. Even if they're adults, you want a food that doesn't encourage excessive growth. I'd lean toward something like Hill's Science Diet Large Breed Adult, which is available in 35 lb and sometimes larger bags. I haven't fed it personally, but the vets I've talked to at checkups mention it enough that it's probably not a terrible choice.
What about keeping costs under control? A lot of people search for best dog food under $200, and what that usually means is finding a quality 40 or 50 lb bag that doesn't require a payment plan. Without tossing out prices I can't verify right now, I'll say this: Diamond Naturals, Purina One, and some of the Victor formulas consistently fall into the "affordable bulk" category at retailers like Chewy and Amazon. You don't need to spend a fortune to get food that meets AAFCO standards and has named meat meals as the first ingredient. I've bought 50 lb bags of Diamond for less than some boutique brands charge for a 12 lb bag. It's not glamorous, but my dogs don't care about marketing.
One thing I wish I'd learned earlier: don't just trust the bag's feeding chart blindly. The PetMD article points out that the chart is a starting point, and your dog's ideal weight is what matters, not their current pudgy weight. I had my shepherd on 4½ cups a day because the bag said so, and he got a little thick around the middle. My vet had me drop it by half a cup and he leaned out. Body condition scoring is boring but it works. I just check that I can feel his ribs without a layer of blubber over them.
If you're overwhelmed, Dog Food Advisor has a tool that supposedly gives you personalized picks in 60 seconds weighted by editorial reviews and nutritionist vetting. I've used it a couple times and it's decent, though I think it leans a bit heavy on the premium stuff. Still, it's a good sanity check if you're staring at a wall of bags at the store.
So here's my quick and dirty take. For a 50 lb dog, you can't go wrong with a mainstream brand like Purina Pro Plan, Blue Buffalo, or Diamond Naturals. Aim for a calorie density around 370-400 kcal per cup and watch your dog's body condition. For a 100 lb dog, the same brands work, but I'd prioritize foods with glucosamine and chondroitin if your dog is older, and definitely stick to dry food unless you hate money. Buy the biggest bag you can store properly. Check the feeding chart, then adjust. And if you're looking at a 50 kg dog, go for a large breed formula and talk to your vet about joint health early.
I didn't mention wet food much because, honestly, for dogs this size it's more of a topper than a main meal. I've used canned pumpkin or a spoonful of wet food to hide pills, but the bulk of their calories comes from kibble. That's just the reality when you've got a dog that outweighs a second grader.
I'll probably update this when I try something new. My neighbor ended up going with the Pro Plan and her Lab is doing fine. No fireworks, just good stools and a shiny coat. Sometimes boring is best.
