Btn-group not stretching width of table - html

Question

I have a table with a table header and a table row. The header is a btn-group, with 12 buttons to resemble months of a calendar, the row is of 31 columns. I want the btn-group to distribute evenly & stretch the full width of the table row. I can add style="width:100px;" to each button, but that's not responsive, and I don't necessarily know the width of the full table.
Can anyone see what I need to add to my code?
<thead>
<tr>
<th colspan="31">
<div class="btn-toolbar" role="toolbar">
<div class="btn-group">
<button type="button" class="btn btn-default">Jan</button>
<button type="button" class="btn btn-default">Feb</button>
<button type="button" class="btn btn-default">Mar</button>
<button type="button" class="btn btn-default active">Apr</button>
<button type="button" class="btn btn-default">May</button>
<button type="button" class="btn btn-default">Jun</button>
<button type="button" class="btn btn-default">Jul</button>
<button type="button" class="btn btn-default">Aug</button>
<button type="button" class="btn btn-default">Sep</button>
<button type="button" class="btn btn-default">Oct</button>
<button type="button" class="btn btn-default">Nov</button>
<button type="button" class="btn btn-default">Dec</button>
</div>
</div>
</th>
</tr>
</thead>
Here is the css tag I changed from the Bootstrap 3 defaults:
.btn-group {
width:100%;
}
.btn-toolbar {
width:100%;
}
If I use btn-group-justified, it looks like this:

Answer 1

Add the following class to the parent container: .btn-group-justified
<thead>
<tr>
<th colspan="31">
<div class="btn-toolbar" role="toolbar">
<div class="btn-group btn-group-justified">
<button type="button" class="btn btn-default">Jan</button>
<button type="button" class="btn btn-default">Feb</button>
<button type="button" class="btn btn-default">Mar</button>
<button type="button" class="btn btn-default active">Apr</button>
<button type="button" class="btn btn-default">May</button>
<button type="button" class="btn btn-default">Jun</button>
<button type="button" class="btn btn-default">Jul</button>
<button type="button" class="btn btn-default">Aug</button>
<button type="button" class="btn btn-default">Sep</button>
<button type="button" class="btn btn-default">Oct</button>
<button type="button" class="btn btn-default">Nov</button>
<button type="button" class="btn btn-default">Dec</button>
</div>
</div>
</th>
</tr>
and for even more reference, read the following part of the documentation:
http://getbootstrap.com/components/#btn-groups-justified