The final installment in my little math lesson:
So we know how to calculate guaranteed analysis section and how to calculate carbohydrates in cat food, now we shall learn how calculating calories in cat food is helpful.
This is important because calories not only come from carbohydrates, which we calculated, but from protein and fat as well. So we need to calculate the total amount of calories.
It is very possible to have a low carbohydrate cat food be high in calories. Usually if carbohydrate count is low, then one of the other two (protein or fat) will be high. Protein higher than fat would be more ideal.
Guaranteed Analysis for dry food:
Crude protein …..min. 30.0%
Crude fat …………min. 23.0%
Crude fiber……….max. 1.0%
Ash ………………….max. 8.0%
Protein = 4
Fat = 9
Carbohydrate = 4
Depending on what source you use, the bolded above may vary. The bolded means that for every gram of protein, that’s 4 calories. For every gram of fat, that’s 9 calories. For every gram of carb, that’s 4 calories. Again, this could vary depending on the source but doing calculations based on what the guaranteed analysis says is not accurate to being with (as they are in minimums and maximums).
Okay, so first thing is first, the formula for getting the carbs (this should look somewhat familiar if you visited the calculating carbohydrates page):
100 – %protein – %fat – %moisture – %ash = carbohydrate
100 – 30 – 23 – 10 – 8 = 29% carbohydrates
So now the important three are:
30% – protein
23% – fat
29% – carbohydrate
So the bolded values are what we multiply each by.
Protein = 30 x 4 = 120
Fat = 23 x 9 = 207
Carbohydrate = 29 x 4 = 116
Add them up: 120 + 207 + 116 = 443
Total calories is 443 for 100g of food.
If we want to put this in kcal/kg, multiply it by 10:
443 x 10 = 4430 kcal/kg
Say the food weighs 150 grams / cup, then here is the formula:
4430/1000 x 150 (grams)
4.43 x 150 = 664.5 kcal/cup
If you want to calculate it in ounces know that 100g=3.5 ounces (or very close to it)
So our original calculation is 443 calories for 100g of food.
443/3.5 = 126.6 calories per ounce of food
If you want to know what percentage of protein, fat, and carb make up the calories divide each by the total amount:
Protein was 120 so 120/443 x 100 = 27.1% of the total amount of calories was from protein
Fat was 207 so 207/443 x 100 = 46.7% of the total amount of calories was from fat
Carbohydrate was 116 so 116/443 x 100 = 26.2% of the total amount of calories was from carbohydrates
If you really want to make sure you did your calculations correctly, protein, fat and carbohydrates must equal 100% so add up the percentages:
27.1% + 46.7% + 26.2% = 100%
Again, we are going by the GA section of the pet food label, they are well known to not be 100% accurate. These are always estimates
But from this calculation, we do know that the biggest source of calories is coming from fat.
(Sorry if this was all confusing, I really tried to go step-by-step so it could be followed easily)