How many Uses or Applications can I get out of a jar of pigment or a pan of eye shadow?

This is a really hard question to answer because our lid sizes, eye shapes, application techniques, brushes, and shadow formulations differ.

I decided to do a little snooping anyway. 

This is by no means scientific, but it's a fun (and hopefully informative) FYI for you!

The Equipment:

• Micro-scale (measures down to 0.01g)
• The Body Shop Eye shadow brush (found the most "medium" brush I could; medium length 1.5cm/0.6" bristles, medium-softness or -spread so it's not extremely fluffy or packed)
• 0.22g of loose pigment (0.02g as buffer for "fallouts" and debris in the brush). Typically, 1.5g of pressed shadow should last you longer than 1.5g of loose pigment.
• Silicone oil to prime my skin surface
• Cotton pads and makeup remover

Each "Application":

• I wanted to make sure my applications were "generous", so each "application" (covering two lids) was represented by approximately 2.5" x 0.7" strip of skin.
• I had to assume this would be equal to or greater than the average person's lid space, from lash-to-brow, of both lids combined.
• The shadow is applied as a wash, over silicone-oil primed skin, in order to maximise pigment adherence from the brush. Again, this should mean I am applying equal amounts of or more pigment than the average person would typically. 
• I allowed fallout and drop-off of pigments because this is typical of the average application. 
• I did a manual count using a notepad, to see how many times I could repeat the application before depleting the 0.2g of pigment.

The results?

0.2g (0.007oz) of powder pigments would give you at least 24 full applications typically. This is not bad at all because if you are like most people and apply your shadows or pigments only to your eyes, instead of all over your face, cheekbones, shoulders, body, etc, you will get quite a lot of uses out of your product.

• This means 1g of powder can give you 120 applications and a typical 1.5g pan of shadow can last you about 180 applications (6 months of once-daily use) depending on how you use it.
• L'oreal Infallible Coleur Shadows should be able to give you about 420 applications because of how densely packed the 3.5g of pigments are, though it might LOOK a lot smaller compared to a MAC jar.
• 4.5g of pigment in a MAC's new jars can give you about 540 applications. This means it should least you for about 1.48 years of daily use unless you have tons of fallout during application.
• 7.5g of pigment in the old MAC pigment jars, however, can give you around 900 applications, so that's the reason why so few people ever seem to finish their old jars.

Important Disclaimers:

1. If you are using a very fluffy brush like a MAC 217 or 224 versus a flatter brush, you will tend to "lose" more product because the bristles are designed for blending and sheering out (i.e. pick up and dust off). If you want a lot of color intensity, instead of applying layers and layers of shadow, wear a good primer so the first coat of pigment goes on and stays on.
2. If you are using a very matte or very glittery shadow or pigment, you will "lose" more product to your brush bristles and to fall-out, because matte shadows don't tend to adhere as well to the skin as metallics and pearls.
3. Please remember that powders vary in texture and weight. Some finer powders will settle and be packed densely, which is why some MAC pigments might look only 1/2 full when they are new. A dense pigment will still give you as many applications as a looser one, so don't worry over-much about the container not being "full".
4. This whole experiment was done in good fun, and because this is something I've been wondering about for years. Findings are approximate and may not be representative of everyone. Individual results will definitely vary based on the above 3 points!

For Buyers Online:

1. For those of you buying samples, note that most sellers sell by volume (quarter-teaspoon for example) rather than weight. If you're getting a more sparkly, gritty pigment like MAC Rose, you WILL be getting less product by weight than a 1/4 tsp of dense pigment like Copper Metal, Rose Gold, etc.
2. If you are buying anything in pressed form, the difference will usually be negligible between shades and textures (as long as they are well-pressed).
3. Is it better to purchase pigments by weight or by volume? It's hard to make a call because you may not know the texture/density a pigment is going to be beforehand.  In general, if you are buying something very glittery and fluffy (e.g. Kitchmas, Blue Brown, Green Brown, Copper Sparkle, Rose, Naked pigments for example), go by weight or opt to buy them in pressed form. If you are buying something that is very metallic and dense (More fine-grained pigments like Silver Metal, Copper Metal, etc) go by volume (spoon sizes, jar sizes etc).

The fairest and most consistent way to buy and sell loose pigments is to go by weight because that is how the raw ingredients are costed for. Unfortunately, it's easier and cheaper to buy a measuring spoon than it is to get a digital micro-scale,  so most sellers continue to sell by volume instead of weight.