A recipe calls for gelatin sheets, your cupboard holds powder, and the dessert waits while you guess. Gelatin forms are interchangeable once you know the weights, but spoon measures and sheet counts hide those weights, which is why conversions go wrong. This calculator converts between powder in grams, powder in teaspoons, sheets, and agar powder, so the form you own becomes the form the recipe needs, with no guessing and no failed set.
The maths rests on three fixed weights. One gelatin sheet weighs about 2.5 grams. One teaspoon of gelatin powder weighs about 3.1 grams. Agar powder is stronger than gelatin by weight: 4 grams of agar set about as firmly as 7 grams of gelatin powder. From those three facts, every conversion follows: multiply sheets by 2.5 to get powder grams, divide powder grams by 2.5 to get sheets, and scale agar by four sevenths of the gelatin weight. The calculator does all of it at once, so you see every form side by side.
Here is a worked example. Your recipe needs 7 grams of gelatin powder, which is one standard packet, and you only have sheets. Divide 7 by 2.5 to get 2.8 sheets, which you round to 3 sheets for a normal dessert. If you have agar instead, multiply 7 by 4 over 7 to get 4 grams of agar powder. If you only have teaspoons, divide 7 by 3.1 to get about 2.3 teaspoons of powder. Small rounding differences matter less than people fear: desserts forgive a sheet or a fraction of a teaspoon either way.
How you handle each form matters as much as the amount. Soak gelatin sheets in plenty of cold water for five minutes until soft, then squeeze out the water and melt the sheets into the warm, not boiling, liquid. Sprinkle powder over cold water, let it sit five minutes until it swells into a spongy mass, then melt it gently. Agar works differently: it must be boiled for one to two minutes to dissolve, and it starts setting around 40 degrees, so work quickly once it is mixed and do not expect to remelt it smoothly.
Agar is the most misunderstood swap in this set. It sets more firmly and less creamily than gelatin, it sets at room temperature instead of in the fridge, and it does not melt in the mouth the same way, which can feel odd in a panna cotta or mousse. Use the converted agar amount for jellies, fruit gels, and vegan desserts, where firmness is welcome. For a silky panna cotta, reduce the agar slightly, by about a quarter, and add a little extra cream, to get closer to the soft gelatin texture.
A few habits prevent the classic gelatin failures. Never boil a gelatin mixture after the gelatin is added, because high heat breaks the proteins and the dessert will not set. Never add gelatin to boiling liquid directly: bloom it first, then melt it into liquid that is warm to the touch. Avoid fresh pineapple, kiwi, papaya, and mango in gelatin desserts, because their enzymes break gelatin down; canned versions are fine, because canning heat destroys the enzymes. With the right conversion and the right handling, the form you own is always the right form.
Gelatin strength is graded by bloom, and most home recipes assume the standard grade, which is why conversions work as simply as they do here. Professional kitchens use bloom numbers from 125 to 250, with higher bloom setting firmer, but supermarket sheets and powder are close enough to standard that the 2.5 gram sheet rule holds. If a recipe from a professional source specifies a bloom grade, follow it rather than converting by weight alone, because a high-bloom gelatin at the same weight sets noticeably firmer. For everyday desserts, though, the sheet and powder weights in this tool are all you need, and the dessert will set as the recipe intends.