What Is Gelatin Bloom Strength?

The definition

Bloom strength is a measure of the rigidity of a gelatin gel. It is determined by the Bloom test: a 6.67% gelatin solution is prepared in water, chilled at 10°C for 17 hours, then measured for the force in grams required to depress the surface 4mm with a standardized 12.7mm plunger. The resulting number is the bloom value. A higher number means a firmer gel.

The grades on this site run from 100 to 265 bloom. The test was developed by Oscar T. Bloom in 1925 and is still the test gelatin is graded by.

The grade scale

The sheet-grade ranges below are the full spread of what 5 published pastry references state; where those references disagree, the figure this site uses is a midpoint and is marked as one. Knox powder is not graded on packaging, but its bloom value is stated by two independent culinary references.

What the sources say

Each reference below was read on 2026-09-21. Where a reference states a range rather than a single figure, the range is shown; a trailing "+" means it gives a minimum only, and "—" means it does not cover that grade. The last column gives the figure this site converts with, and whether every reference states it or the site is taking a midpoint of the spread.

• Titanium: Sources give 100 and 120; the site uses 115, inside that spread.
• Bronze: Sources give 125, 140 and a 125–155 range; the site uses 135, inside that spread.
• Platinum: Sources give 250, a 235–265 range and "230+"; the site uses 240, inside that spread.

Why bloom strength matters for conversion

Bloom is a rigidity reading taken at one fixed concentration, and a gel's rigidity rises with roughly the square of concentration. Substituting one grade for another at the same weight therefore produces a measurably different result — a softer or firmer set depending on the direction of the swap.

The adjustment formula is: recipe quantity × (recipe bloom ÷ your bloom)^0.5. If a recipe calls for 6g of 200-bloom gold gelatin and you have Knox (~225 bloom), you need 5.7g. If you have silver sheets (~160 bloom), you need 6.7g. Why the square root, and where the straight ratio disagrees.

Knox and store-bought powder

Most US store-bought gelatin powder — including Knox Unflavored Gelatin, the most common consumer brand — is approximately 200–225 bloom. Knox specifically is widely cited at ~225 bloom across independent cooking references, though the manufacturer does not print this value on retail packaging.

When a recipe says "1 packet of gelatin" without specifying bloom, it is assumed to mean Knox or an equivalent US grocery powder. When a recipe gives a bare weight in grams without specifying a bloom, and the recipe is from a European source, it typically assumes gold sheets at approximately 200 bloom.

These unstated assumptions are the source of most gelatin substitution errors. Knowing the bloom value — even an approximate one — removes the guesswork.

Why consumer packaging doesn't list bloom

Bloom strength is an industrial specification designed for food manufacturers and professional pastry operations, not home cooks. Bakeries ordering gelatin in bulk specify bloom as a quality parameter. Consumer packaging skips it because home cooks historically used gelatin from a single source (one brand, one format) and never needed to convert between grades.

The rise of translated European pastry books and internet recipes from professional kitchens changed that. A reader in the US following a French pastry blog needs to know that "5 feuilles de gélatine" likely means 5 silver or gold sheets — and how to convert that into Knox packets with the right amount.

Frequently asked questions

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