Edit in JSFiddle

<!-- modal 구동 버튼 (trigger) -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#mySmallModal">
  작은 Modal
</button>
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#myModal">
  기본 Modal
</button>
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#myLargeModal">
  큰 Modal
</button>

<!-- 작은 Modal -->
<div class="modal fade" id="mySmallModal" tabindex="-1" role="dialog" aria-labelledby="mySmallModalLabel">
  <div class="modal-dialog modal-sm" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title" id="myModalLabel">작은 Modal 제목</h4>
      </div>
      <div class="modal-body">
        작지 않아!
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">닫기</button>
      </div>
    </div>
  </div>
</div>

<!-- 기본 Modal -->
<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title" id="myModalLabel">기본 Modal 제목</h4>
      </div>
      <div class="modal-body">
        Size don't matter.
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">닫기</button>
      </div>
    </div>
  </div>
</div>

<!-- 큰 Modal -->
<div class="modal fade" id="myLargeModal" tabindex="-1" role="dialog" aria-labelledby="myLargeModalLabel">
  <div class="modal-dialog modal-lg" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title" id="myModalLabel">큰 Modal 제목</h4>
      </div>
      <div class="modal-body">
        나는 관대하다
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">닫기</button>
      </div>
    </div>
  </div>
</div>