Measuring & Weighing
Judging from email messages, the most common point of confusion for those just getting started in pyrotechnics seems to be measuring & weighing.
To begin with here are two important points:
1. EVERYTHING is measured by weight, not by volume.
2. The amounts of chemicals in ALL formulas are in percentage (all the parts total up to 100).
Now we'll explain what these 2 points mean:

For example, lets say you have the following formula:
( this isn't an actual formula for anything )

This simply means this mixture is made from 1/2 Zinc Dust and 1/2 Sulfur Powder
 (50% Zinc Dust & 50% Sulfur Powder).
You can mix 50 grams of Zinc & 50 grams of Sulfur, or 50 ounces of Zinc and 50 ounces of Sulfur, 100 grams of Zinc & 100 grams of Sulfur, or even 200 tons of Zinc and 200 tons of Sulfur.
All the measurements are 50% of each chemical, and they will all work.
You CANNOT use 1 Tablespoon of Zinc and 1 Tablespoon of Sulfur, or 1 cup of Zinc and 1 cup of Sulfur.
Why? Because these are VOLUME measurements.
The reason is that different chemicals weigh different amounts.
1 Tablespoon of Zinc weighs 68 grams and 1 Tablespoon of Sulfur weighs 12 grams.
In the correct formula above there are equal amounts of Zinc & Sulfur. If you measured by volume, say 1 Tablespoon of each, you would wind up with over five times more Zinc by weight than Sulfur.
Your formula wouldn't work.
To make things worse, volume measurements are not constant. A tablespoon of Zinc dust may in fact weigh 68 grams today, but may weigh 50 grams or possibly 75 grams tomorrow. Why?... because fine powders compact when they sit around (making a tablespoon of it weigh more than it did before), and "fluff up" when disturbed or shaken (making a tablespoon of it weigh less than it did before).
Only weight measurements can be used in chemistry & pyrotechnics.
ALL formulas are measured by weight, usually in grams.

Here's an actual formula for a white star...

Make things easy on yourself... there are no complex calculations necessary.
To make the above formula, you would just mix 64 grams of potassium nitrate, 14 grams of antimony sulfide, 18 grams of sulfur and 4 grams of dextrin.
If you wanted to make twice as much... just double all the numbers.
If you want to make half as much... just cut all the numbers in half.

Now that you've got how to measure chemicals down, we need to talk about accuracy.
You CANNOT use a cheap spring-type postal scale for measuring chemicals.
If you want to get involved with pyrotechnics, you need the proper tools, and to measure the various amounts of chemicals in these formulas, you need an accurate  Gram scale, preferably accurate to 1/10th gram, although a scale accurate to 1/2 gram is still usable.
Digital Gram Scales and Triple Beam Balances are your best bets.

We now carry a line of affordable digital scales that can be found
in our "Pyrotechnic Equipment" section.