Carbohydrates don’t need to be listed on the label of pet foods in Australia, but we can use a simple calculation to offer us a rough idea. It’s not perfect, and I’ll explain why, but the following method is how to calculate carbohydrates in a pet food:
100 – Protein % – Fat % – Moisture % – Ash %
Here’s a carbohydrate calculator for dog food and cat food for your convenience. If moisture and ash are not listed on your pet food, you may use average values of 10% moisture and 8% ash:
The above calculator will give you a rough idea, but there's a little more to it than that.
Other factors to consider are undisclosed moisture and ash percentages and variance from min & max percentages.
Moisture & Ash
Moisture and ash are usually listed, but as these percentages aren't required to be listed we can use an average 10% moisture and 8% ash for dry food only. Wet foods contain significantly more moisture.
Min & Max
We often find percentages are listed with a guaranteed minimum or maximum. This makes our simple calculation somewhat vague. If a pet food contains Protein (min) 20% then it's possible the protein, on average, is higher.
How to Calculate Carbohydrates: An example
Let's say a dry dog food contains 20% protein, 10% fat, 10% moisture, and 8% ash:
100 - 20 - 10 - 10 - 8 = 52
This product would contain approximately 52% carbohydrates.
So that's it, that's how to calculate carbohydrates in a pet food.