How much fragrance oil is left? Subtract the batches.

The short answer

• What is left in the bottle is what you bought minus what every batch took, and the recipe already says how much a batch takes. You do not weigh it to find out.
• Weigh it once a month anyway. The gap between the books and the scale is your waste, and it goes into the recipe as a percentage.
• Count what is left in batches, not ounces, and reorder when fewer are left than you will pour before the new bottle arrives, plus one.

You do not need to weigh the jug to know what is in it. You bought 80 oz, the recipe takes 6 oz a batch, and you have poured eight batches since it arrived, so 32 oz is left, less the little that clings to the pitcher each time. That subtraction is the answer on any weekday. The scale is a check you run once a month to find out how much "the little" is. The number you want at the end is how many more batches the jug will pour, because that is what decides when to order the next one.

Why not just weigh the bottle?

Because you would have to weigh every bottle, every jug and every bag, every week, and the number is stale the moment you pour again. A maker with thirty materials cannot keep that up, so they weigh the two or three that worry them and guess at the rest. The masking-tape habit, writing the full weight on the bottle the day it arrives, is the right idea done by hand: it turns the bottle into a number you can subtract from. The recipe is the other half. It already says what one batch takes, so every batch you make is one subtraction, and the running total is what is left.

Everything in that subtraction is a weight. Fragrance oil is sold by weight rather than volume, and so is wax; a candle maker's guide to measuring supplies says so in as many words (Armatage Candle Company, 6 March 2025, checked 20 September 2026). A fragrance load is a percentage of the wax's weight, and the scale reads weight. One unit from the invoice to the pour, and nothing to convert. If a supplier does sell by volume, convert once, on the day the bottle arrives, and track it in weight from then on.

What does the subtraction look like?

One jug, one recipe, eight batches. This is a worked example, not anyone's real numbers.

That is the whole method, and a spreadsheet with three columns does it: what came in, what each batch took, what is left. The catch is the phrase "on paper". The recipe says 6.0 oz because that is what goes into the tins. It is not what leaves the jug.

What do you do when the scale disagrees?

Find out by how much, then stop it happening again. Once a month, put the jug on the scale. To read it you need the jug's own weight, and the cheap way to get that is to weigh the full jug the day it arrives and subtract the label: this one weighed 84.4 oz full, the label says 80, so the empty jug is 4.4 oz. Write that on the jug.

Today the scale reads 34.0 oz. Take off the jug: 34.0 − 4.4 = 29.6 oz of fragrance. The books said 32.0. The difference, 32.0 − 29.6 = 2.4 oz, went where fragrance goes over eight batches: the film left in the pouring pitcher, the measuring cup, the drips down the side of the jug, the one tin that ran heavy. It is the gap between what the recipe puts in the tins and what the jug gives up to fill them.

Spread over the batches it is 2.4 ÷ 8 = 0.3 oz a batch, and 0.3 ÷ 6.0 = 5% of the recipe line. Two things follow.

First, book it. The 2.4 oz is gone, so the books should say so. A stock count, which is what a stocktake is, removes the ounces the scale could not find and takes their value out with them: at $1.20 an ounce, 2.4 × $1.20 = $2.88 leaves your inventory. It was never going to be in a candle.

Second, put the 5% into the recipe as waste, so that from now on each batch takes 6.0 × 1.05 = 6.3 oz off the shelf instead of 6.0. At the next count the books and the scale should land within a few tenths of each other, and if they do not, the percentage moves. The number to chase is a difference near zero at the next count, whatever percentage gets you there.

How many batches are left?

Four, not five. With the honest per-batch figure, 29.6 ÷ 6.3 = 4.7, and you cannot pour seven tenths of a batch. The paper said five.

The drift costs more than $2.88. It costs a pour you planned, with the wax melted and the wicks set, that comes up an ounce or two short of the one thing you cannot substitute. The same thing shows up across the jug's life: the label divides to 80 ÷ 6.0 = 13.3 batches, and the jug actually pours 80 ÷ 6.3 = 12.7. A jug you counted as thirteen batches is twelve.

Counting in batches is also the only form of the number that is any use. "29.6 oz" tells a candle maker nothing until they divide it; "four batches" is two weeks of pours.

When do you reorder, counted in batches?

When fewer batches are left than you will pour before the new jug arrives, plus one. You pour twice a week and the supplier takes ten days from order to doorstep, so 10 ÷ 7 × 2 = 2.9, call it three pours while you wait. The plus one is because you only look at the jug on pour day: the shelf drops in whole batches, so you notice a line only after you have crossed it.

Four batches, then: 4 × 6.3 = 25.2 oz. Set the reorder line there, or at 26 to keep it a whole number. From today's 29.6 oz the next pour leaves 23.3, which is below the line, so that is the day you order. Three more pours take 3 × 6.3 = 18.9 oz, leaving 4.4 oz in the jug when the new one lands.

Set the line at three batches instead, 18.9 oz, and the arithmetic is tight in the wrong place: you cross it after two pours, at 17.0 oz, order that day, and the three pours before the delivery need 18.9. The third one is 1.9 oz short. Hence the plus one.

Reorder line	You order at	Pours before it lands	Left when it lands
3 batches, 18.9 oz	17.0 oz	3	1.9 oz short
4 batches, 25.2 oz	23.3 oz	3	4.4 oz

The textbook version of this rule is daily use times lead time plus a safety margin. For a maker who pours in batches it is the same rule in the unit you actually think in, and the plus one is the safety margin.

Does the 5% change what a candle costs?

By three cents a tin. Fragrance was 6.0 × $1.20 = $7.20 a batch, $7.20 ÷ 12 = $0.60 a tin; with the waste in the recipe it is 6.3 × $1.20 = $7.56 a batch and $7.56 ÷ 12 = $0.63 a tin. Nobody re-prices a candle for three cents, and that is fine. The waste line exists to make the shelf count true, and an untrue shelf count costs you the short pour above.

The $1.20 is the average cost of what is in the jug, and when the next jug arrives at a different price the two get averaged by quantity; that sum has its own post. The count in this post and the cost in that one are the two halves of one figure: what is on the shelf, and what it is worth.

By hand, the whole method is a column per material and the discipline of writing down every batch on the day you pour it, and the discipline is what slips first. In Trackost, a jug goes in as a purchase in the unit you track it in, ounces here; the recipe line carries its quantity and a waste percentage; completing a batch takes that quantity, with the waste, off each material; a stocktake adjustment removes the ounces the scale could not find, at cost; and the reorder line you set on each material, in ounces, puts it on the low-stock list when the shelf crosses it, netting off anything already on order.

Questions

Is fragrance oil sold by weight or by volume?

By weight, at the suppliers that state it, and wax is sold the same way. A fragrance load is a percentage of the wax's weight and a kitchen scale reads weight, so nothing in the method needs converting. If a supplier does sell by volume, convert once when the bottle arrives, using the density on its data sheet, and track it in weight from then on.

How often should I weigh the bottle?

Once a month is enough for most materials, plus once before a big production run. Each count tells you how far the books drifted since the last one; if it is under half a percent, count that material less often and spend the time on the one that drifts more.

What if the scale shows more than the books say?

Then the recipe line overstates what a batch takes, or you have been pouring light. Book the difference as a positive stock count and lower the waste percentage. The aim is the same either way: a difference near zero at the next count.

Does this work for wax, oils and lye, not just fragrance?

Yes, for anything you use by weight, and wax is where the ounces are biggest. Things you use by count, wicks, jars, lids, drift less because nothing clings to a pitcher, but a batch still takes its number of them off the shelf the same way.

One bottle goes into three recipes. Does the method still work?

Yes. Each recipe has its own fragrance line, each batch of each recipe subtracts its line, and the bottle's balance is what is left after all of them. Weigh it the same way. The waste percentage belongs on each recipe's line, since a 4 oz batch and a 12 oz batch do not lose the same amount.