How to read the guaranteed analysis like a pro: the dry-matter trick
The guaranteed analysis, called the analytical constituents in Europe, is the block of percentages on a pet food label that lists guaranteed levels of a few nutrients: crude protein, crude fat, crude fibre, crude ash and sometimes moisture (AAFCO, 2024). Owners reach for these numbers to compare foods, and almost everyone reads them wrong, because the figures are printed on an as-fed basis, water included. A wet food at 78 per cent water mechanically shows lower percentages than a kibble, even when it is the richer food once the water is removed (AAFCO, 2024). The single skill that turns a confused label-reader into a confident one is converting both foods to a dry-matter basis, which strips out the water and lets you compare like with like. This article teaches that conversion with worked numbers.
Last updated :General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.
Why the printed numbers mislead
The percentages are honest, but they describe the food as it sits in the bag or tin, water and all. Since wet food is mostly water and kibble is mostly not, the two cannot be compared directly. A kibble printing 30 per cent crude protein and a wet food printing 10 per cent crude protein look, at a glance, like a clear win for the kibble. That impression is an artefact of moisture, not a fact about protein.
The fix is to imagine each food with all its water evaporated, leaving only the dry substance, and to express the nutrient as a percentage of that. This is the dry-matter basis, and it is the only fair way to compare foods of different moisture content. Veterinary and labelling sources agree that cross-reading the constituents after converting to dry matter is what avoids the confusion (AAFCO, 2024).
The two formulas you need
Two pieces of arithmetic do all the work, and both are simple enough to run on any label.
First, find the dry matter. Dry matter percentage equals 100 minus the moisture percentage. A kibble at 8 per cent moisture is 92 per cent dry matter; a wet food at 78 per cent moisture is 22 per cent dry matter.
Second, convert any nutrient. The dry-matter rate equals the printed rate divided by the dry-matter percentage, multiplied by 100.
That is the entire method. If moisture is not printed, a reasonable default is about 10 per cent for dry food and about 78 per cent for wet, though using the actual figure is always better.
The worked example that flips the ranking
Apply the formulas to the example above and the apparent ranking reverses.
| Food | Printed (as-fed) protein | Moisture | Dry matter | Protein on a dry-matter basis |
|---|---|---|---|---|
| Kibble | 30% | 8% | 92% | (30 / 92) x 100 = 32.6% |
| Wet food | 10% | 78% | 22% | (10 / 22) x 100 = 45.5% |
The wet food calculation is (10 divided by 22) multiplied by 100, which is about 45.5 per cent. So the kibble printing the higher headline number, 30 per cent against 10, is in fact the leaner food on a dry-matter basis: 32.6 per cent against 45.5 per cent. The "lower" wet food is the richer one once water is removed (AAFCO, 2024). An owner comparing the two as printed would have reached the opposite of the truth.
Alt text: "Worked panel showing as-fed protein percentages converted to dry-matter values, reversing the ranking of a kibble and a wet food."
The percentages do not measure quality
A second professional habit is knowing what the guaranteed analysis cannot tell you. The constituents set bounds, not a quality measure. Crude protein counts nitrogen, and nitrogen can come from a highly digestible animal source or from a poorly usable one; the number alone does not distinguish them. The analytical constituents tell you how much of certain nutrients are present, not how good those nutrients are or how well the animal can absorb them (WSAVA, 2021). That is why the guaranteed analysis is read alongside the ingredient list and the nutritional adequacy statement, not on its own. A high protein figure on a dry-matter basis is a promising signal, not a proof of quality.
The ingredient-percentage trap
The same as-fed problem reappears in the highlighted ingredient percentages on the front of a bag. A claim of "30% chicken" usually means 30 per cent at the moment of mixing, when fresh meat still holds about 70 per cent water (FEDIAF, 2019; AAFCO, 2024). After drying, that 30 per cent fresh chicken can contribute only about 9 per cent of the finished kibble. The reliable cue is the form of the ingredient tied to the figure: a percentage on a meal or a dehydrated protein is worth more, value for value, than the same percentage on fresh meat, because the meal is already dehydrated and stable (AAFCO, 2024). Reading the form alongside the figure is what separates a meaningful claim from a flattering one.
Estimating the carbohydrate the label leaves out
A second professional move addresses something the guaranteed analysis never prints: carbohydrate. Most labels declare protein, fat, fibre, ash and sometimes moisture, but they rarely state the carbohydrate content directly. It can be estimated by difference, a calculation known as nitrogen-free extract, or NFE. The NFE percentage equals 100 minus the moisture, crude protein, crude fat, crude fibre and crude ash percentages (AAFCO, 2024). Whatever is left after accounting for everything else is, broadly, the carbohydrate.
This estimate is approximate, because it absorbs the measurement slack of every other figure, but it is good enough to compare foods and to spot a kibble that is far higher in carbohydrate than its marketing implies. For a cat in particular, an obligate carnivore, the carbohydrate-by-difference figure can be a more revealing number than the headline protein, and it is invisible to anyone who only reads the printed constituents. Running the subtraction, ideally on a dry-matter basis so the moisture does not distort it, is part of what separates a thorough label-reader from a casual one.
The ash figure and what it really signals
A figure that worries owners unnecessarily is crude ash, sometimes called inorganic matter. Ash is simply what remains when a food is fully combusted: the mineral content, including calcium, phosphorus and the trace minerals. A higher ash figure is not a sign of poor quality or of literal ash in the food; it usually reflects mineral-rich ingredients such as bone or organ tissue. The number becomes worth a glance only in specific contexts, for example where mineral intake is being managed for a urinary or kidney condition, and even then it is the specific minerals, not total ash, that matter.
The general point is that each line of the guaranteed analysis answers a narrow question and is easy to over-read in isolation. Crude protein counts nitrogen without grading its source. Crude fibre captures one fraction of the indigestible matter, not all of it. Crude ash totals the minerals without naming them. Read individually and literally, these figures invite the wrong conclusions; read together, on a dry-matter basis, and cross-checked against the ingredient list and the adequacy statement, they become a genuine comparison tool. The skill is as much knowing what each number cannot say as knowing how to convert it.
A practical label routine
Three moves turn the guaranteed analysis from a source of confusion into a comparison tool:
- Find the moisture figure, or use the defaults, and calculate dry matter for each food you are comparing.
- Convert each nutrient you care about to a dry-matter basis with the divide-and-multiply formula, then compare the foods only on those converted numbers.
- Cross-read the converted figures against the ingredient list and the nutritional adequacy statement, remembering that the percentages bound the nutrients but do not grade their quality.
Once the conversion becomes automatic, the most common label mistakes, mistaking a wet food for weak or assuming the higher printed number is the richer food, simply stop happening.
Why minimums and maximums matter
A detail that separates a careful reader from a casual one is noticing the direction of each guarantee. Crude protein and crude fat are declared as minimums, meaning the food contains at least that much, while crude fibre and crude ash are declared as maximums, meaning the food contains no more than that (AAFCO, 2024). This is not a quirk; it reflects which way a shortfall would matter. The guarantee tells you the floor for nutrients you want present and the ceiling for components you want limited.
The practical consequence is that the printed protein figure may understate the food's actual protein, since the real content sits at or above the stated minimum. Two foods printing the same minimum could differ in their true protein, which is one more reason the guaranteed analysis is a comparison starting point rather than a precise measurement. For an owner this is mostly a caution against over-interpreting small differences between the printed numbers of two foods: a one-point gap in declared protein, on figures that are floors rather than exact values, is well within the noise. The conversion to a dry-matter basis remains worthwhile, but it converts guarantees, not exact assays, and reading them as the bounds they are keeps the comparison honest.
Where to read more (read guaranteed)
The questions on the guaranteed analysis, why moisture changes the reading, and how to compare two foods on a dry-matter basis are handled in our reading and decoding a label FAQ and our choosing and judging quality FAQ. For structured help, the reading the macronutrient profile guide and the how to read pet food comparison tools guide walk through the conversion step by step. The basis itself is defined in our entry on as-fed versus dry-matter basis.
Putting the whole reading together
A confident reading of a label braids three blocks rather than reading any one in isolation. The guaranteed analysis gives the numbers, once converted to a dry-matter basis and read as the bounds they are. The ingredient list describes the materials those numbers came from, with named species and forms carrying more information than generic terms. And the nutritional adequacy statement certifies that the food meets a life stage and says how that was substantiated. No single block answers the question of whether a food suits an animal; together they come close.
The reason professionals lean on the dry-matter conversion is that it unlocks the first block and lets it speak honestly alongside the other two. Without it, the numbers mislead the moment moisture differs, and the whole reading tilts. With it, an owner can compare a wet food and a kibble fairly, judge whether a high protein figure is backed by named animal sources, and confirm the food is complete for the right life stage. That sequence, convert then cross-read, turns a label from a marketing surface into the most reliable source of information a buyer has.
The takeaway (read guaranteed)
The guaranteed analysis is printed on an as-fed basis, so its percentages mislead the moment two foods differ in moisture, and they make wet food look weak when it is often the richer choice. One conversion fixes it: divide the printed rate by the dry-matter percentage and multiply by 100, then compare only the converted numbers. Add the knowledge that these figures bound nutrients without grading them, and an owner reads the label like a professional rather than guessing from the front of the bag.