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dry ferts: how many grams in a tsp?!

832 Views 6 Replies 7 Participants Last post by  Jalopy
i keep getting different answers...
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Because different substances have different weights per the same volume: a teaspoon of feathers is not = to a teaspoon of iron.

There are many calculators on the web.

As mentioned, the densities of various chemicals will be different, so there is no single answer to your question.
Why not just get a gram scale for you measurements? A quick search on the term should give you several options, and some are only about $10 - $15, well within the range of most hobbyists. That way your get a lot more accuracy too.
Gram is a measurement of how much something weighs. Teaspoons is a measure of how much space it takes. Your missing factor is density

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i keep getting different answers...
Probably because there is no perfect answer. YANC used to have the teaspoon weight of each compound. I was going to provide the link for you. However, it was just changed (1 month ago) based on volume = mass/density which does not account for dead space in volume measures. I contacted the author and explained the error.

Here are some of the more common weights. Let me know if you need any others.

KNO3 = 5,200mg
KH2PO4 = 5,600mg
K2SO4 = 6,400mg
Plantex = 4,300mg

Since particle size, purity and how much moisture has been absorbed an exact answer is impossible. All the measures above are approximations which is close enough for our purposes.

If you want to be more exact you can calculate the amount of a compound in a saturated water solution. Example, look up the solubility of KNO3 in a solubility table. At 20 degrees celcius 100ml of water will become solute with 33 grams of KNO3. So if you make a solution like that one teaspoon will contain roughly 6.6 grams of KNO3.
DFS has a scale that has a spoon extension. It's pretty handy.
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