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This is probably the one thing where it's hard to figure because of a lack of consensus and/or knowledge.  When I brought this up to our vet several days ago, she had no idea.  You have to remember that veternary students learn what the commercial pet food industry wants them to learn about nutrition and feeding.

So how do you know how much to feed?  Trial and error.  I mentioned about weighing and keeping track of your pet's weight in my post Some Considerations.  That is an absolute must, otherwise you will not know if you're feeding too much or too little.

Another way to determine if your pet needs to lose, gain or maintain weight is by body shape and feel.  With your dog standing up, look down from overhead.  The body should have a sort of hour glass shape.  If there are no curves, your dog is probably overweight.  If the curves are excessive, your dog may need to gain weight.

Additionally, while the dog is standing, feel their rib area.  You should be able to easily feel the ribs without a lot of effort or mushing down.  If you can't feel the ribs at all and need to press down to find them, your dog probably needs to lose weight.  If you can easily feel the ribs, but there is no padding whatsoever and the ribs obviously stand out visually, your dog may need to gain weight.  A dog at approximately its ideal weight will not have obviously visible ribs, and a "light" layer of fat over the ribs when you feel them.

Next time you take your dog to the vet, have them show you this is as I know reading this method may not make sense without visuals and hands on.  If you have a PetSmart with Banfield vet in your area, they should have a chart posted by the scale that shows the overhead body views.  One of the techs there will be happy to show and explain about feeling the ribs (assuming they aren't swamped and/or you don't mind waiting).

I (and my vet) totally recommend this visual and touch check.  Weight can fluctuate periodically, which is perfectly normal, but can be frustrating if your dog needs to lose or gain weight.  And each dog, even within the same breed, is different, so general weight guidelines may not apply.  Mixed breeds have a blend of genetics, so it's difficult to give a figure as an ideal weight.

Now on to amounts.  Again, there is no real consensus among the information I've found in my research.  And if you check dog food bags, you will see wide ranges for the weights and feeding amounts.  So where to start?

Two of the recommended feeding amounts I've seen are 2-3% of body weight and 1/4 to 1/2 pound of food per 10 pounds of body weight.  To illustrate the difference in these, I'll use Sassy's ideal weight of 50 pounds.

2% of 50# = 16oz/1#
2.5% of 50# = 20oz/1.25#
3% of 50# = 24oz/1.5#

Per 10 pounds of weight, so the multiplier is 5:
1/4# x 5 = 20oz/1.25#
1/2# x 5 = 40oz/2.5#

Quite a bit of difference, yes?  And then on top of this, you have addtional considerations:
* Age (pup, adult, senior)
* Activity Level (low, moderate, high)
* Pregnant or Lactating

To put this into words as a sort of illustration, let me do a quickie comparison of our dogs:
* Angel - 5/6 months, very active
* Merlin - 12 months, very active
* Sassy - 24 months, low to moderately active (due to hip dysplasia)

So Angel and Merlin need more food due to age and activity level, while Sassy needs less due to activity level.  Additionally, Sassy needs to lose 6 pounds to bring her to the bottom of her ideal weight range because of the hip dysplasia.  If using the percentage calculations, I would use 2% for Sassy (weight loss) and either 2.5 or 3% for Angel and Merlin (maintenance for age/activity level).  

I'm not comfortable with the "per 10 pounds of weight" method, especially for Sassy since she needs to lose weight.  If she were at her ideal weight of 50 pounds, AND pregnant or lactating, then I probably would go with the 1/2# per 10.  Pregnant and lactating animals need more calories and nutrients to support their condition.

Since I have just started preparing our pack's food, this is about the only insight I can give at this time.  I will post updates periodically to show progress, tweaking, etc.

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After feeding the pack this new way for several days, I am definitely comfortable with using 2-4% of body weight to determine the number of ounces of food to give each.  Angel, being a highly active 6 month old, is getting about 3.7%.  Merlin, a very active 12 month old, is getting about 2.8-2.9%.  Sassy is getting 2% since she needs to lose weight, although she is more active as the antibiotic works on her UTI and she's recovered from her hips being stretched out for x-rays.  

So far all 3 are chowing the meals, including Sassy who used to be the last one to finish.  They all get a baby carrot as a snack several times a day, and some days they get some fresh apple or pear if daddy or I are in the mood to eat one and share it with them.