Looking at the specifications for 3 of 9 (aka Code 39) barcodes in the link I posted earlier, it states that x>=.19mm. In barcode nomenclature, "X" is the width of the thinnest bar/space in a barcode pattern, so the 3 of 9 spec says that X cannot be less than .19mm in order to have a reasonable assurance that a scanner can accurately scan and decode the barcode.
For 3 of 9 barcodes, bars and spaces can also be 2X or 3X wide. The bar & space patterns always take up 15 * X, plus one additional X for the thin space between adjacent barcode patterns. A single 3 of 9 barcode pattern always begins and ends with a bar and contains 5 bars and 4 spaces.
Therefore, the minimum total width of a 3 of 9 barcode character pattern is (15+1) * 0.19mm = 3.04mm
A 3 of 9 barcode must begin and end with start/stop characters (patterns). For many barcode styles, the start and stop patterns are different from one another, but for 3 of 9 they are the same. The purpose of the start & stop patterns is to tell the scanner if the barcode has been read left-to-right (correct side up) or right-to-left (upside-down), so that the entire barcode pattern can be successfully decoded.
A 3 of 9 barcode may contain a checksum character. If included, it always precedes the stop character.
You state the maximum character length of the barcode pattern is 15 characters. You did not state whether or not this includes the start/stop characters and the optional checksum, but for sake of this exercise let's assume 15 characters is the length of the complete barcode.
In order to be able to assure the 3 of 9 barcode is readable, the minimum width of a 15-character barcode is: 15 * 3.04mm = 45.6mm.
You have 32mm available to you, so to be able to squeeze the barcode into the available space, you must reduce the scale by nearly 30%, which is a pretty significant reduction. My guess is that a scanner will not be able to read and decode it at that scale. To use the 3 of 9 barcode style, you must reduce the maximum character count to 32mm / 3.04mm = 10 characters, or use wider labels.
Admittedly, the 3 of 9 barcode style has poor "density"... it requires a generous number or bars & spaces (16 * X) to encode a single character. I don't know if you are able to utilize an alternative barcode style. If the data being encoded is limited to digits only, there are other styles with better "density" (2 of 5 Interleaved, for example) and may allow you to produce a scannable barcode that contains 15 characters in only 32mm. The URL I posted earlier should be helpful, and there are other similar web sites that can be found.
HTH, John
