The one-line answer: a barcode holds a short number, a QR code holds the message itself. The stripes on a cereal box encode thirteen digits that mean nothing until the shop's system looks them up. A QR code can carry a whole web address, a Wi-Fi password or a contact card, and any phone can read it with no lookup at all. That difference decides nearly every practical question about which one to use. The question that matters is who is scanning, with what device, and whether the code has to do anything beyond being read.

This is the plain version: what each kind of code holds, who can read it, and which one fits a retail product, a stock label, an event ticket or a poster. It also says what this site makes and what it doesn't. We make QR codes. We don't make retail barcodes, and if that's what you need, you'll know where to get one by the end.

What a barcode actually holds

The familiar barcode is a one-dimensional code: a row of bars and gaps of different widths, read straight across. Because it's only read in one direction, it can only hold a little, usually a short string of digits.

EAN-13 and UPC-A are the codes on retail products. EAN-13 holds 13 digits and UPC-A holds 12, and in both the last digit is a check digit that lets the scanner catch a misread. The number is a product identifier, called a GTIN, and that's all it is. The price, the name and the stock count live in the shop's database, keyed on that number.
Code 128 and its relatives hold short runs of letters and numbers. You see them on shipping labels, warehouse shelves and asset tags. Again, what they hold is a reference, an ID that some other system knows the meaning of.

That's the key thing about a barcode: it's a key, not a message. Scan a product barcode with nothing behind it and you get a number. That's exactly what a till wants, because the till already has the database. It's useless to a customer standing in the aisle.

Barcodes are read by dedicated scanners: the laser or imaging scanner at a checkout, or a handheld gun in a warehouse. Phone cameras mostly don't read them natively. Some apps do, Google Lens among them, but the built-in camera on most phones looks for QR codes and ignores bars.

What a QR code actually holds

A QR code is a two-dimensional code. It stores data in a grid of square modules, read across and down, so it holds far more in the same space. At its largest size and lowest error correction, the standard allows up to 7,089 digits, 4,296 letters and numbers, or 2,953 bytes of arbitrary data. In practice a code holds far less, because more data means smaller squares, and smaller squares mean a code that has to be printed bigger or scanned closer.

Two things follow from that extra room.

The message travels with the code. A QR code can contain the full address of a web page, so the phone that reads it knows where to go without asking anyone. It can also hold Wi-Fi details, a contact card or plain text. No database is needed on the reading side.
It survives damage. QR codes carry error correction at one of four levels, which let roughly 7%, 15%, 25% or 30% of the pattern be lost and still read. A barcode's check digit only detects a bad read. It can't repair one. Codes made on this site default to level M, about 15%, which survives a scuff or a thumbprint without making the pattern denser than it needs to be. You can raise it in the design settings if the code is going somewhere rough.

And they're read by phones. Every recent iPhone and Android phone reads a QR code with the camera it shipped with, no app, which is why QR codes took over everything aimed at the public. How to scan a QR code covers the details and what to do when one won't read.

Is a QR code a barcode?

Technically, yes. "Barcode" is the family name for any machine-readable optical code, and the QR code is one of several 2D barcodes. The others you're likely to have met:

Data Matrix, a small square code common on electronic components, medical packaging and other places where space is tight.
PDF417, a stacked, wide rectangle of rows, used on many driving licences and airline boarding passes.
Aztec, a square code with a bullseye in the middle, common on mobile boarding passes and rail tickets.

So when someone says "barcode" they usually mean the striped one-dimensional kind, and when a company announces "2D barcodes" it usually means QR codes or one of their cousins. Everything below uses "barcode" in the everyday sense: the stripes.

Side by side

Shape: barcode is a row of bars, read across. QR code is a square grid, read across and down.
Holds: barcode usually holds 8 to 13 digits on retail products, or a short ID string elsewhere. QR code holds up to a few thousand characters, in practice a web address or a short block of data.
What the data is: barcode holds a key that needs a database to mean anything. QR code holds the message itself.
Who reads it: barcodes are read by checkout and warehouse scanners. QR codes are read by any modern phone camera, and by most modern imaging scanners too.
Damage: a barcode's check digit detects errors. A QR code's error correction repairs them.
Who issues it: retail barcodes need a number licensed from GS1. Anyone can make a QR code.

Which one does the job need?

A product sold in shops: a retail barcode, from GS1

If a product is going through someone else's till, it needs a real GTIN, and that number comes from GS1, the not-for-profit standards body that runs the retail numbering system. A barcode generator will happily draw the bars for any number you type. The drawing is the easy part. A retailer's system only accepts a number your business has licensed. A made-up number will scan and then fail to match, or worse, match somebody else's product.

The QR code on the same box does a different job: it's the code for the customer, not the till. It opens instructions, ingredients, a reorder page or a warranty form. QR codes on product labels covers that half, including how small you can print it.

The two are converging. GS1 runs a programme to get checkout scanners reading 2D codes, built on a standard called GS1 Digital Link, a QR code that carries the product number in a web address. One code can then serve the till and the customer's phone. It needs a licensed GTIN like any retail code. This site doesn't create GS1 Digital Link codes, and a plain QR code from any generator isn't one.

Stock, shelves and asset tags: whichever your scanners read

For labels only your own team scans, the honest answer is whatever your hardware already reads. If the warehouse runs on handheld laser guns, a Code 128 label is the right call and a QR code adds nothing. If the people scanning are using phones (a field engineer, a hire customer, a volunteer at a stock-take), a QR code is the one their camera will actually see, and it can open a page instead of just returning an ID. QR codes on equipment and maintenance logs is about exactly that setup.

Event tickets: the shape of the code is not what makes it a ticket

"Barcode ticket" is a phrase that hides two very different things.

A ticket that admits someone has a code that's unique to that ticket and checked against a list at the door. The first scan marks it used and the second is refused. That code can be a barcode, a QR code, PDF417 or Aztec. The format barely matters. What makes it a ticket is the system behind it: the list of valid codes, and the door app that checks each one off. Without that system, a printed code is a picture, and it will let in a photocopy as happily as the original. That's why admission codes come from a ticketing platform, not a code generator.

A ticket can also carry a code that informs: it opens the schedule, the venue map, parking and door times. That code doesn't need to be unique, because it's the same for everyone, and it's the job a QR code is built for. It's also the one worth making dynamic, so that when the stage times move, the printed tickets still open the right page.

Most well-run events print both: the platform's admission code, and a QR code beside it for everything else. The event ticket template builds the second one and says plainly what it can't do.

Posters, packaging, menus and anything aimed at the public: QR

If the person scanning is a member of the public holding their own phone, it's a QR code. Nobody carries a barcode scanner, and a barcode carries nothing a phone could open anyway. This covers almost everything people mean by "putting a code on it". Where should a QR code point is the next decision.

Shipping parcels: neither, it's the carrier's label

Parcel labels carry the carrier's own barcodes, generated by the carrier's system when you buy postage, because only that system knows the tracking number. Don't make your own. You can add a QR code to the packing slip inside the box for returns or reorders, which is the customer's code again.

What this site makes, and what it doesn't

It makes QR codes: links, Wi-Fi, contact cards, text and the rest. One static code is free. Paid plans add more static codes and dynamic ones, whose destination you can change after printing. See pricing for exactly what each plan includes.
It doesn't make one-dimensional barcodes: no EAN, UPC or Code 128.
It doesn't issue product numbers or GS1 Digital Link codes. Those start with GS1.
It doesn't validate tickets. A code made here can't be marked as used. Bulk generation from a spreadsheet exists on the Business plan, but it produces static link codes, up to 200 per batch, with no check-in behind them. That suits printing one code per seat or per item. It doesn't replace a ticketing platform.

The short version

A barcode is a key; a QR code is the message. Barcodes need a database to mean anything. QR codes carry the content with them.
Barcodes are for scanners, QR codes are for phones. Pick by who's holding the device.
Selling through retailers? You need a licensed GTIN from GS1. A drawing of a number is not a product barcode.
Admitting people to an event? You need a ticketing system, whatever shape its code takes. Use a QR code alongside it for the schedule and the map.
Talking to the public? QR code, dark on light, tested on a cheap phone before the print run.

→ Make the "everything else" code for your tickets