Bootstrap Carousel Full Screen

This is how I did it. This makes the images in the slideshow take up the full screen if it´s aspect ratio allows it, othervice it scales down.

.carousel {
    height: 100vh;
    width: 100%;
    overflow:hidden;
}
.carousel .carousel-inner {
    height:100%;    
}

To allways get a full screen slideshow, no matter screen aspect ratio, you can also use object-fit: (doesn´t work in IE or Edge)

.carousel .carousel-inner img {
    display:block;
    object-fit: cover;
}

Update Bootstrap 4

Bootstrap 4 has utility classes that make it easier to create a full screen carousel. For example, use the min-vh-100 class on the carousel-item content...

<div class="carousel slide" data-ride="carousel">
      <div class="carousel-inner bg-info" role="listbox">
            <div class="carousel-item active">
                <div class="d-flex align-items-center justify-content-center min-vh-100">
                    <h1 class="display-1">ONE</h1>
                </div>
            </div>
      </div>
</div>

Full screen carousel demo

This works to make the carousel items full screen, but carousel items that contain images or videos that have a specific size & aspect ratio require further consideration.

Since the viewport h/w ratio is likely to be different than the image or video h/w ratio, usually background images or object-fit are commonly used to size images and videos to "full screen". For videos, use the Bootstrap responsive embed classes as needed for the video ratio (21:9, 19:9, etc...).

Full screen videos demo

Also see: https://stackoverflow.com/a/58765043/171456

Original answer (Bootstrap 3)

Make sure the img inside the carousel item is set to height and width 100%. You also have to make sure the carousel and any of the .item containers (html,body) are 100%...

html,body{height:100%;}
.carousel,.item,.active{height:100%;}
.carousel-inner{height:100%;}

Boostrap 3 Full Screen Carousel Demo

Here's an example for Bootstrap 3.x: http://www.codeply.com/go/2tVXo3mAtV

You can do it without forcing html and body to me 100% height. Use view port height instead. And with mouse wheel control too.

function debounce(func, wait, immediate) {
  var timeout;
  return function() {
    var context = this,
      args = arguments;
    var later = function() {
      timeout = null;
      if (!immediate) func.apply(context, args);
    };
    var callNow = immediate && !timeout;
    clearTimeout(timeout);
    timeout = setTimeout(later, wait);
    if (callNow) func.apply(context, args);
  };
}

var slider = document.getElementById("demo");
var onScroll = debounce(function(direction) {
  //console.log(direction);
  if (direction == false) {
  	$('.carousel-control-next').click();
  } else {
  	$('.carousel-control-prev').click();
  }
}, 100, true);

slider.addEventListener("wheel", function(e) {
  e.preventDefault();
  var delta;
  if (event.wheelDelta) {
    delta = event.wheelDelta;
  } else {
    delta = -1 * event.deltaY;
  }

  onScroll(delta >= 0);
});

.carousel-item {
  height: 100vh;
  background: #212121;
}

.carousel-control-next,
.carousel-control-prev {
  width: 8% !important;
}

.carousel-item.active,
.carousel-item-left,
.carousel-item-right {
  display: flex !important;
  justify-content: center;
  align-items: center;
}

.carousel-item h1 {
    color: #fff;
    font-size: 72px;
    padding: 0 10%;
 }

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>


<div id="demo" class="carousel slide" data-ride="carousel" data-interval="false">

  <!-- The slideshow -->
  <div class="carousel-inner">
    <div class="carousel-item active">
      <h1 class="display-1 text-center">Lorem ipsum dolor sit amet adipisicing</h1>
    </div>
    <div class="carousel-item">
      <h1 class="display-1 text-center">Inventore omnis odio, dolore culpa atque?</h1>
    </div>
    <div class="carousel-item">
     <h1 class="display-1 text-center">Lorem ipsum dolor sit</h1>
    </div>
  </div>

  <!-- Left and right controls -->
  <a class="carousel-control-prev" href="#demo" data-slide="prev">
    <span class="carousel-control-prev-icon"></span>
  </a>
  <a class="carousel-control-next" href="#demo" data-slide="next">
    <span class="carousel-control-next-icon"></span>
  </a>

</div>

I found an answer on the startbootstrap.com. Try this code:

CSS

html,
body {
    height: 100%;
}

.carousel,
.item,
.active {
    height: 100%;
}


.carousel-inner {
    height: 100%;
}

/* Background images are set within the HTML using inline CSS, not here */

.fill {
    width: 100%;
    height: 100%;
    background-position: center;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
}

footer {
    margin: 50px 0;
}

HTML

   <div class="carousel-inner">
        <div class="item active">
            <!-- Set the first background image using inline CSS below. -->
            <div class="fill" style="background-image:url('http://placehold.it/1900x1080&text=Slide One');"></div>
            <div class="carousel-caption">
                <h2>Caption 1</h2>
            </div>
        </div>
        <div class="item">
            <!-- Set the second background image using inline CSS below. -->
            <div class="fill" style="background-image:url('http://placehold.it/1900x1080&text=Slide Two');"></div>
            <div class="carousel-caption">
                <h2>Caption 2</h2>
            </div>
        </div>
        <div class="item">
            <!-- Set the third background image using inline CSS below. -->
            <div class="fill" style="background-image:url('http://placehold.it/1900x1080&text=Slide Three');"></div>
            <div class="carousel-caption">
                <h2>Caption 3</h2>
            </div>
        </div>
    </div>

Source