What read distance can you realistically promise a client?
Promise contact. A figure in centimetres, measured on your phone with a gesture you have practised, is the one number certain to disappoint. Specify the gesture and the device population instead, because those are what actually determine whether a deployment works.
Why a number is the wrong commitment
Any distance you measure depends on the phone, the case, the mounting surface and the person holding it. Change any one and the figure changes.
You measured on a phone you know, holding it the way you know works, on a tag lying on a desk. The deployment will be a stranger's phone, in a case, on a mounted tag, held for half a second.
So the number is not a lie and it is not transferable. Quoting it creates an expectation that the first field failure will contradict, and after that the whole deployment looks unreliable.
What to commit to instead
The gesture. "Touch the phone to the marked area" is a commitment you can meet, verify and demonstrate.
The device population. "Works on phones with NFC from the last several years, including with a standard case" is more useful than any distance, and it is the thing clients actually worry about.
The conditions. Naming the mounting surface matters, because the same tag on wood and on a steel door are different products, and one of them needs an on metal tag.
The failure behaviour. Saying that a tag needs a moment of contact, rather than a wave, sets an expectation people can act on.
How to demonstrate honestly
Hand your phone to someone else, or better, use theirs. A demonstration you perform yourself proves only that you know where the antenna is.
Demonstrate on the real surface, at the real mounting height, with the real tag. A sample on a table has told the client nothing about a tag on a painted steel column.
Show a failure deliberately. Presenting the phone edge on, or too fast, and then correcting it, teaches the client what the technology is and protects you from the first complaint.
Wording that survives
Avoid a distance in a specification unless you are prepared to test it on every device the client will bring, on the real surface, and defend it.
Write the requirement as an outcome: a person presenting a phone to the marked area gets the intended result. That is testable and it is what the client actually wants.
If a distance is contractually unavoidable, quote a conservative one measured on the weakest phone available, on the real mounting, and state those conditions alongside it.
Where a client genuinely needs range beyond contact, say early that phones do not deliver it. A dedicated reader with a large antenna is a different project, and discovering that after installation is far more expensive than discovering it in a meeting.
Frequently asked questions
Can I promise a few centimetres?
Only with the conditions attached, and only if measured on the weakest phone on the real mounting. Without those, it is a figure that will be contradicted in week one.
What if the client insists on a number?
Give a conservative one with its measurement conditions written next to it, and add the gesture requirement. A number without conditions is a commitment you cannot control.
Does a bigger tag let me promise more?
It buys tolerance rather than distance, which is usually what the client actually wants. Neither turns a contact technology into a proximity one.
How do I set expectations with the public?
A printed target and a short instruction on the tag do most of the work. People aim at a symbol and wave at a blank surface.