Code 128 vs Code 39: Which Barcode Format to Choose

Head-to-head comparison

	Code 128	Code 39
Character set	All 128 ASCII characters	43: A to Z, 0 to 9, and - . space $ / + %
Density	High (Code C packs 2 digits per symbol)	Low (wide bars and spaces)
Check digit	Mandatory, modulo 103	Optional, modulo 43
Print tolerance	Needs decent print quality	Survives cheap printers and rough labels
Typical use	Shipping, logistics, asset labels	Military, automotive, nameplates
Best for new projects	Yes, the default pick	Only when required

Code 128: the compact workhorse

Code 128 comes in three character sets. Set A covers uppercase, digits, and control codes. Set B covers the full printable ASCII range including lowercase. Set C encodes pairs of digits, so a 20-digit number takes only 10 symbols, which is why Code 128 dominates shipping labels full of tracking numbers.

Every Code 128 symbol ends with a mandatory modulo-103 check character. Here is a real example encoding A1 in Set B. The start character for Set B has value 104. A has value 33 and sits in position 1; 1 has value 17 and sits in position 2. The weighted sum is 104 + (33 x 1) + (17 x 2) = 104 + 33 + 34 = 171. Then 171 mod 103 = 68, and value 68 in Set B is the character d. So the full symbol is Start-B, A, 1, check character d, Stop. The scanner recomputes this on every read and rejects the scan if it does not match, which catches nearly all misreads.

Code 39: the rugged veteran

Code 39 is simpler and older. Each character is self-contained, the bars are wide, and the format tolerates photocopies, dot-matrix printers, and scratched nameplates. That ruggedness is why MIL-STD-1189 and the automotive industry standardized on it decades ago, and those standards keep it alive today.

Its check character is optional and uses modulo 43. Encoding A1: A has value 10 and 1 has value 1, so the sum is 11. Then 11 mod 43 = 11, and value 11 is B. A Code 39 symbol for A1 with a check character reads *A1B*, where the asterisks are the start and stop characters.

How to tell them apart visually

Code 39 symbols look airy: wide bars, wide gaps, and usually asterisks visible in the human-readable text. Code 128 symbols look dense: narrow bars packed tightly, with no asterisks. If the label holds lowercase letters or punctuation, it cannot be Code 39, since Code 39 has no lowercase.

Which should you choose?

• New inventory, asset, or shipping labels: Code 128. Smaller symbols, full character set, mandatory check digit, universal scanner support.
• Long numeric strings: Code 128 with Set C, which doubles numeric density.
• Harsh environments or legacy systems: Code 39, when the spec sheet or the customer demands it.
• Military or automotive contracts: Code 39, because the standards say so.

Ready to print? Generate Code 128 or Code 39 free: type your text, pick a size, and download a print-ready PNG with correct check characters.