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I am developing a form where the user needs to enter the maximum number of allowed things. Zero is a legitimate value meaning that none are allowed.

I need to find a special value to indicate that there is no limit (using a number slider is, unfortunately, not an option).

Which could be the best alternative among the following ones?

  • Leaving the field blank means unbounded; note that this may conflict with a user request to make the field mandatory
  • Use -1 as the special value
  • Use N as the special value
  • Use 99,999 or something like that as the special value

Here is a mockup showing each alternative.


download bmml source – Wireframes created with Balsamiq Mockups

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Have a look at a related question with some good answers as well… – Janne Aukia May 29 '15 at 12:23
up vote 8 down vote accepted

You should add a check box that indicates that the number of things are limited.
(Thus: An unchecked box indicates that there are unlimited number of items).


download bmml source – Wireframes created with Balsamiq Mockups

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Good idea. You could also use an opposite solution. Create a checkbox with the label "There is no limit of maximum allowed items." If most users want to specify the maximum amount this should be the default state and vise versa. – Tony Bolero Oct 7 '13 at 9:39
@Tony: Definitely :-) – Jørn E. Angeltveit Oct 7 '13 at 9:58

If you change Max number of FOO to Available FOO (or something of that kind) you can use dropdown list with 3 options:

  • Not allowed
  • Up to... + input field to enter max value
  • Unbounded

This is more readable for users unless you have specially prepared audience.

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