How many tubes you will get
Updated
A planning number you should establish once by filling and weighing, then reuse.
Weight, not volume
A tube is specified by volume and your balm is filled by weight, and the two meet through the density of your formula.
So the useful number is not the tube's stated capacity. It is how many grams of your formula that tube actually holds, which you find by filling five, weighing them and taking the average.
Establish it per formula and per tube supplier, because both move it.
The arithmetic
Tubes = batch weight in grams, minus losses, divided by grams per tube.
If a tube holds 4.5 g and you make 300 g with 5 percent loss, that is 285 divided by 4.5, or about 63 tubes.
Work backwards for a target: 500 tubes at 4.5 g is 2,250 g of product, about 2,370 g of batch after losses, which is several pours rather than one.
What you lose
Residue in the melting pot and the pouring vessel, which is proportionally worse on small batches.
The second pour reserve, if you do not use it all.
Spillage and wiped-off excess.
Five percent is a reasonable starting assumption and ten is realistic for a first batch. Measure your own by weighing the empty pot before and the dirty pot after.
Checking it
Weigh ten filled tubes from a run and look at the spread, not just the average.
A wide spread means inconsistent pouring, which is a yield problem and a net weight problem at the same time, and the net weight is the one printed on the label.