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


2 Answers 2


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

  • 2
    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. Commented Oct 7, 2013 at 9:39
  • @Tony: Definitely :-) Commented Oct 7, 2013 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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