The short answer
The familiar 20-cigarette pack follows a packaging rule, not just a custom. UK government guidance sets a minimum pack size for cigarettes. It also requires a specific pack shape. This article is AI-assisted and draws only on the UK legislation and government guidance quoted in it.
The sources describe what the rules require. They give no official reason for the chosen minimum, so this article does not offer one. The same guidance states the shape requirement for cigarette packs.
What counts as a unit packet
The regulations define a "unit pack" carefully. It is the smallest individual packaging in which a product is, or is meant to be, presented for retail sale. This holds even if the packaging is presented inside a larger container pack. A transparent wrapper is not counted.
The regulations also say which sides are the front and back of a pack. These are the two largest surfaces of the pack that are visible before it is opened. That wording matters because several other rules refer to those surfaces.
The 20-cigarette minimum
The GOV.UK packaging checklist lists the minimum as one of the requirements for a standard pack of cigarettes. It says the pack must hold at least 20 cigarettes. The checklist presents this alongside the other requirements on the pack's shape and surfaces.
The number of cigarettes can appear on the pack in a limited way. The checklist says it may be printed in figures, and the standardised packaging regulations permit text stating the number contained in the packet. Hand rolling tobacco has a weight minimum instead, set at 30 grams for a unit packet.
The cuboid shape requirement
A footnote to the tobacco regulations explains where the shape rule comes from. It says the standardised packaging regulations provide that a unit pack of cigarettes must be cuboid in shape. The footnote adds that this implements an article of the Tobacco Products Directive.
The checklist repeats the point in plain terms. Cigarette packs must be cuboid, while hand rolling tobacco packs may be cuboid, a pouch or cylindrical. Slim cigarette packets are listed among the things a pack must not be, although slim cigarette sticks are allowed.
Surface rules that go with the shape
The shape rule sits alongside rules on how the pack surfaces must look and feel. Under the standardised packaging regulations, any surface of the external or internal packaging of a cigarette packet must be smooth and flat. It must also have no ridges, embossing or other irregularities of shape or texture.
The checklist summarises this by saying the pack must be cuboid with smooth surfaces and no texture or embossing. Taken together, the rules fix a minimum content and a plain, flat-sided cuboid form for the unit packet.
Sources
- legislation.gov.uk (legislation.gov.uk)
- legislation.gov.uk (legislation.gov.uk)
- Tobacco and herbal product packaging rules checklist (GOV.UK)