因为有许多不同的屏幕尺寸总是在变化，最有可能总是在变化，最好的方法是根据你的设计来设置断点和媒体查询。

要做到这一点，最简单的方法是抓取你完成的桌面设计，并在浏览器中打开它。慢慢缩小屏幕，使其更窄。观察设计什么时候开始“断裂”，或者看起来可怕和局促。此时需要一个带有媒体查询的断点。

通常为台式机、平板电脑和手机创建三组媒体查询。但是，如果你的设计在这三个方面都很好，为什么要麻烦地添加三个不同的不必要的媒体查询呢?根据需要来做!

这不仅仅是关于分辨率，你还需要找到设备的DPR: whatismyscreenresolution “设备像素比(DPR)是设备制造商提供的一个数字，用于HiDPI(每英寸高点数)或Retina(苹果的商标)显示器。”

媒体查询示例:(最小分辨率:3.0dppx)

这不是像素数的问题，而是屏幕上字符的实际大小(以毫米或英寸为单位)的问题，这取决于像素密度。 因此，“min-width:”和“max-width:”是无用的。 关于这个问题的完整解释如下: 设备像素比到底是什么?

“@media”查询会考虑像素数和设备像素比，从而产生“虚拟分辨率”，这是你在设计页面时必须考虑的问题:如果你的字体固定宽度为10px，“虚拟水平分辨率”为300 px，那么一行就需要30个字符。

在我看来，这些是最好的断点:

@media (min-width:320px)  { /* smartphones, portrait iPhone, portrait 480x320 phones (Android) */ }
@media (min-width:480px)  { /* smartphones, Android phones, landscape iPhone */ }
@media (min-width:600px)  { /* portrait tablets, portrait iPad, e-readers (Nook/Kindle), landscape 800x480 phones (Android) */ }
@media (min-width:801px)  { /* tablet, landscape iPad, lo-res laptops ands desktops */ }
@media (min-width:1025px) { /* big landscape tablets, laptops, and desktops */ }
@media (min-width:1281px) { /* hi-res laptops and desktops */ }

编辑:改进工作更好的960网格:

@media (min-width:320px)  { /* smartphones, iPhone, portrait 480x320 phones */ }
@media (min-width:481px)  { /* portrait e-readers (Nook/Kindle), smaller tablets @ 600 or @ 640 wide. */ }
@media (min-width:641px)  { /* portrait tablets, portrait iPad, landscape e-readers, landscape 800x480 or 854x480 phones */ }
@media (min-width:961px)  { /* tablet, landscape iPad, lo-res laptops ands desktops */ }
@media (min-width:1025px) { /* big landscape tablets, laptops, and desktops */ }
@media (min-width:1281px) { /* hi-res laptops and desktops */ }

在实践中，许多设计师将像素转换为ems，很大程度上是因为ems提供更好的缩放效果。在标准缩放1em == 16px时，将像素乘以1em/16px得到ems。例如，320px === 20em。

对于这条评论的回应，最小宽度是“移动优先”设计的标准，即你从设计最小的屏幕开始，然后添加不断增加的媒体查询，直至越来越大的屏幕。

无论您是喜欢min-、max-还是它们的组合，都要认识到规则的顺序，记住，如果多个规则匹配同一个元素，后面的规则将覆盖前面的规则。

Extra small devices (phones, up to 480px) Small devices (tablets, 768px and up) Medium devices (big landscape tablets, laptops, and desktops, 992px and up) Large devices (large desktops, 1200px and up) portrait e-readers (Nook/Kindle), smaller tablets - min-width:481px portrait tablets, portrait iPad, landscape e-readers - min-width:641px tablet, landscape iPad, lo-res laptops - min-width:961px HTC One device-width: 360px device-height: 640px -webkit-device-pixel-ratio: 3 Samsung Galaxy S2 device-width: 320px device-height: 534px -webkit-device-pixel-ratio: 1.5 (min--moz-device-pixel-ratio: 1.5), (-o-min-device-pixel-ratio: 3/2), (min-device-pixel-ratio: 1.5 Samsung Galaxy S3 device-width: 320px device-height: 640px -webkit-device-pixel-ratio: 2 (min--moz-device-pixel-ratio: 2), - Older Firefox browsers (prior to Firefox 16) - Samsung Galaxy S4 device-width: 320px device-height: 640px -webkit-device-pixel-ratio: 3 LG Nexus 4 device-width: 384px device-height: 592px -webkit-device-pixel-ratio: 2 Asus Nexus 7 device-width: 601px device-height: 906px -webkit-min-device-pixel-ratio: 1.331) and (-webkit-max-device-pixel-ratio: 1.332) iPad 1 and 2, iPad Mini device-width: 768px device-height: 1024px -webkit-device-pixel-ratio: 1 iPad 3 and 4 device-width: 768px device-height: 1024px -webkit-device-pixel-ratio: 2) iPhone 3G device-width: 320px device-height: 480px -webkit-device-pixel-ratio: 1) iPhone 4 device-width: 320px device-height: 480px -webkit-device-pixel-ratio: 2) iPhone 5 device-width: 320px device-height: 568px -webkit-device-pixel-ratio: 2)

用于常见设备断点的媒体查询

/* Smartphones (portrait and landscape) ----------- */
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) {
/* Styles */
}

/* Smartphones (landscape) ----------- */
@media only screen and (min-width : 321px) {
/* Styles */
}

/* Smartphones (portrait) ----------- */
@media only screen and (max-width : 320px) {
/* Styles */
}

/* iPads (portrait and landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) {
/* Styles */
}

/* iPads (landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) {
/* Styles */
}

/* iPads (portrait) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) {
/* Styles */
}
/**********
iPad 3
**********/
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}

@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}
/* Desktops and laptops ----------- */
@media only screen  and (min-width : 1224px) {
/* Styles */
}

/* Large screens ----------- */
@media only screen  and (min-width : 1824px) {
/* Styles */
}

/* iPhone 4 ----------- */
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) and (orientation : landscape) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}

@media only screen and (min-device-width : 320px) and (max-device-width : 480px) and (orientation : portrait) and (-webkit-min-device-pixel-ratio : 2) {
/* Styles */
}

/* iPhone 5 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 568px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

@media only screen and (min-device-width: 320px) and (max-device-height: 568px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

/* iPhone 6 ----------- */
@media only screen and (min-device-width: 375px) and (max-device-height: 667px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

@media only screen and (min-device-width: 375px) and (max-device-height: 667px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

/* iPhone 6+ ----------- */
@media only screen and (min-device-width: 414px) and (max-device-height: 736px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

@media only screen and (min-device-width: 414px) and (max-device-height: 736px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

/* Samsung Galaxy S3 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 2){
/* Styles */
}

/* Samsung Galaxy S4 ----------- */
@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 3){
/* Styles */
}

@media only screen and (min-device-width: 320px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 3){
/* Styles */
}

/* Samsung Galaxy S5 ----------- */
@media only screen and (min-device-width: 360px) and (max-device-height: 640px) and (orientation : landscape) and (-webkit-device-pixel-ratio: 3){
/* Styles */
}

@media only screen and (min-device-width: 360px) and (max-device-height: 640px) and (orientation : portrait) and (-webkit-device-pixel-ratio: 3){
/* Styles */
}