Crude Ash in Cat Food: What 6–10% DM Tells You

Crude ash is what is left when a feed sample is burned at 550 °C for 2 hours: the mineral fraction that does not combust. On a dry matter basis most complete cat foods sit at 6–10% DM, and that range is normal, not a warning. A number of 12% DM is high but not automatically a bad food, and a number of 4% DM is low enough to ask what is missing.

What the Number Actually Measures

The assay is simple and old. A weighed sample goes into a muffle furnace at 550 °C for about 2 hours, the organic matter burns off as carbon dioxide and water, and the residue is weighed. Whatever is left is reported as crude ash: calcium, phosphorus, magnesium, potassium, sodium, chloride and trace minerals, plus sand or grit if the batch was contaminated.

Two limits follow from that method. Ash is not a measure of total mineral content, because some minerals volatilize at 550 °C and are lost. And ash says nothing about which minerals are present or in what ratio — 8% ash from bone and 8% ash from a mineral premix give the same number on the label.

6–10% DM: The Usual Band

Convert before you compare. Labels report as-fed percentages, and a canned food at 78% moisture with 1.6% ash as-fed is 7.3% DM; a dry food at 10% moisture with 6.6% as-fed is also 7.3% DM. Comparing the two as-fed figures (1.6 versus 6.6) is the single most common mistake in this whole topic.

The formula is ash% DM = ash% as-fed ÷ (100 − moisture%) × 100. That is it. One line of arithmetic, and the label finally says something you can use.

Food type	Ash % DM	Moisture %	Ca:P
Canned pâté, chicken	6.5	78	1.2:1
Dry food, chicken and rice	7.0	10	1.1:1
Raw with bone (80/10/10)	9.5	70	1.4:1
Fish-based dry food	10.5	10	1.3:1
Renal diet, canned	6.0	78	1.1:1

Two rows in that table are worth a second look. The raw diet at 9.5% DM gets there from ground bone, not from a premix, and the fish-based dry food at 10.5% DM usually reflects a high fish meal inclusion plus added phosphates.

The 2 Sources of Ash

Almost all of the number comes from 2 places. The first is skeletal: bone in raw mixes, bone meal, and meat-and-bone meal in rendered ingredients. A diet with 10% ground bone by weight lands near 9–10% DM ash without anything being added. The second is a mineral premix: calcium carbonate, monocalcium phosphate, sodium chloride, and trace mineral salts, typically 1–3% of the formula. A chicken-based dry food with no bone in the ingredient list still shows 6–8% DM ash, and that ash is the premix.

3 Ways the Number Gets Misread

First, ash treated as a quality score. It is a residue, not a grade; a 10% DM raw food built on bone is not worse than a 6% DM extruded food built on starch. Second, ash treated as equal to calcium. Calcium is usually 1.0–1.6% DM in a complete food while total ash is 6–10% DM, so ash is roughly 5–8 times the calcium figure and cannot stand in for it. Third, ash compared across moisture levels, which is the 1.6 versus 6.6 error above and makes canned food look dangerously low in minerals.

There is a fourth, quieter misread: a very low ash number read as proof of quality. Below about 5% DM, the question is not purity but adequacy — which mineral was left out to get there.

4 Label Checks That Beat the Ash Figure

Check the moisture line and convert every value to DM before comparing 2 foods; without that step the comparison is meaningless.
Check the calcium and phosphorus lines, not just ash, and look for a Ca:P between 1.0:1 and 1.5:1 for an adult maintenance diet.
Check the ingredient list for bone, bone meal, and meat-and-bone meal, which tell you the ash came from skeleton rather than a premix.
Check whether the guaranteed analysis is typical or minimum/maximum: a maximum ash of 10% with a typical of 7% is a different food from one that always runs at 10%.

Water content shifts every other number on the label, which is why the moisture line is checked first in the water content guide; carbohydrate by difference depends on ash as well, and that arithmetic is walked through in the carb content guide.

When Ash Deserves a Call to the Vet

Ash matters clinically in 2 situations. A cat with chronic kidney disease or a history of struvite stones needs the phosphorus and magnesium figures, not the ash total, and those targets come from the vet. And a cat eating a raw diet at 9.5% DM ash with a Ca:P of 1.4:1 may be fine, while the same diet fed without bone to a growing kitten is a different calculation.

If a food lists ash above 12% DM, or the calcium line is missing entirely, ask the maker for the full mineral panel. A manufacturer that cannot supply calcium, phosphorus and magnesium in % DM is not hiding a secret; it usually has not measured them.

One last practical note: ash is stable. It does not degrade in storage, so an ash figure is one of the few label numbers you can trust across a 12-month shelf life, unlike vitamin A or taurine. That makes it a useful anchor when you compare 2 batches of the same product.

Terms mentioned in this article

Frequently asked

Is 12% ash in cat food dangerous?

Not by itself. It is above the usual 6–10% DM band, and it should be checked against the calcium and phosphorus lines, but bone-rich raw diets routinely run 9–10% DM and are not toxic. The number only means something next to a mineral panel.

Does high ash mean low quality?

No. Ash is a lab residue, not a grade. A 10% DM raw food built on ground bone and a 6% DM extruded food built on starch are simply different formulas, and neither number tells you the protein source or digestibility.

How do I compare ash in a canned food with a dry food?

Convert both to dry matter first: ash% DM = ash% as-fed divided by 100 minus moisture, times 100. A canned food at 1.6% as-fed with 78% moisture is 7.3% DM, which matches a dry food at 6.6% as-fed with 10% moisture.