PPI and DPI make absolutely no difference to how a document will print off a browser. the printer takes no information on screen dot pitch or the DPI of the images etc. if you are printing images they would print at a size similar in proportion to how they are displayed on screen. the print processor of the browser would increase the DPI of the images from something rather low like 72dpi to whatever DPI the rest of the document is. say the image displays as half a page wide, then its about 4" wide physically. the pixel width of the image would be approx 300px to display correctly in the browser. by the time it prints at a nominal 300DPI, the processor has added pixels and the image will grow to around 1200px which at 300 DPI is 4".

当涉及到矢量或非基于像素的元素，如文本，打印机从驱动程序中选择自己的DPI，这与屏幕点间距或浏览器宽度无关。如果浏览器宽度为3000px，打印处理器将适当地换行文本。

heres what makes it hard about creating print displays: each browser and printer will interpret text sizes (pt, em, px) and spacing in its own way. depending on what printer, browser and maybe even OS you use, you will get a different amount of lines and characters per page. so even if you test on your computer using your browser and printer and figure out that you can display the text in a box at 640x900px and its perfect on print, the next guy who tries to print will possibly get it printing differently. there really is no way to force each printer and browser to get it identical each time.

忘记像素，更忘记DPI，你唯一可以使用像素的事情是设置一个表宽度，模拟打印机上可打印区域的宽度。在这种情况下，我发现640px宽是接近的。

从技术上讲，您可以这样做，但是要让所有浏览器打印出与屏幕上显示的一模一样的页面，需要做很多工作。而且，大多数浏览器强制在打印结果上输入URL、打印日期和页码，这并不总是理想的。这不能被改变或禁用。

相反，我建议根据屏幕上的内容创建一个PDF，并将PDF提供给下载和/或打印。虽然大多数可用的PDF库都是付费的，但也有一些免费的替代方案可用于创建基本的PDF。

我在谷歌上搜索“A4 CSS页面模板”(codepend .io)后看到了这个解决方案。它使用<page>标记在浏览器中显示A4 (A3,A5，也是纵向)大小的区域。在这个标记中显示内容，但绝对位置仍然相对于浏览器区域。

身体{ 背景:rgb (204204204); ｝ 页面{ 背景:白色; 显示:块; 保证金:0自动; margin-bottom: 0.5厘米; 箱影:0 0 0.5cm rgba(0,0,0,0.5); ｝ 页面(=“A4大小){ 宽度:21厘米; 高度:29.7厘米; ｝ 布局页面(大小= " A4 "][=“肖像”]{ 宽度:29.7厘米; 高度:21厘米; ｝ @media print { 正文，页{ 保证金:0; 不必:0; ｝ ｝ <页面大小= >“A4 A4页面< / > <page size="A4" layout="portrait">A4 portrait</page>

这适用于我没有任何其他css/js库包括在内。适用于当前的浏览器(IE, FF, Chrome)。

I know that this subject is quite old but I want to share my experience about that topic. Actually, I was searching a module that can help me with my daily reports. I'm writting some documentations and some reports in HTML + CSS (instead of Word, Latex, OO, ...). The objectif would be to print them on A4 paper to share it with friends, ... Instead of searching, I decided to have a small funny coding session to implement a simple lib that can handle "pages", page number, summary, header, footer, .... Finally, I did it in ~~2h and I know that's not the best tool ever but it's almost ok for my purpose. You can take a look at this project on my repo and don't hesitate to share your ideas. It's maybe not what you are searching for at 100% but I think that this module can help you.

基本上我创建了一个页面的主体“宽度:200mm;”和容器的高度:290mm(小于A4)。然后我使用了page-break-after: always;因此，浏览器的“打印”选项知道何时拆分页面。

回购:https://github.com/kursion/jsprint

A4尺寸为210x297mm

所以你可以用CSS设置HTML页面来适应这些大小:

html,body{
    height:297mm;
    width:210mm;
}

很久以前，在2005年11月，AlistApart.com发表了一篇文章，讲述他们如何只用HTML和CSS就出版了一本书。参见:http://alistapart.com/article/boom

以下是那篇文章的节选:

CSS2有一个分页媒体(如纸张)的概念，而不是连续媒体(如滚动条)。样式表可以设置页面大小和页边距。页面模板可以指定名称，元素可以声明它们希望在哪个命名的页面上打印。此外，源文档中的元素可以强制换页。下面是我们使用的样式表的一个片段:

@page {
    size: 7in 9.25in;
    margin: 27mm 16mm 27mm 16mm;
}

由于是一家美国出版商，我们的页面大小以英寸为单位。我们，作为欧洲人，继续使用公制测量。CSS两者都接受。

设置好页面大小和页边距后，我们需要确保在正确的位置有换页符。下面的摘录显示了如何在章节和附录之后生成分页符:

div.chapter, div.appendix {
    page-break-after: always;
}

此外，我们使用CSS2来声明命名页面:

div.titlepage {
    page: blank;
}

也就是说，扉页要印在标有“空白”的页上。CSS2描述了命名页面的概念，但只有当页眉和页脚可用时，它们的价值才会显现出来。

无论如何……

既然你想打印A4，你当然需要不同的尺寸:

@page {
    size: 21cm 29.7cm;
    margin: 30mm 45mm 30mm 45mm;
     /* change the margins as you want them to be. */
}

这篇文章深入探讨了设置换页等问题，所以你可能想要完整地阅读它。

在您的例子中，诀窍是首先创建打印CSS。大多数现代浏览器(>2005)支持缩放，并且已经能够显示基于打印CSS的网站。

Now, you'll want to make the web display look a bit different and adapt the whole design to fit most browsers too (including the old, pre 2005 ones). For that, you'll have to create a web CSS file or override some parts of your print CSS. When creating CSS for web display, remember that a browser can have ANY size (think: “mobile” up to “big-screen TVs”). Meaning: for the web CSS your page-width and image-width is best set using a variable width (%) to support as many display devices and web-browsing clients as possible.

编辑(26-02-2015)

今天，我碰巧在SmashingMagazine上看到了另一篇最近的文章，这篇文章也探讨了如何使用HTML和CSS进行打印设计……

编辑(30-10-2018)

这引起了我的注意，因为它的大小不是有效的CSS3，这确实是正确的-我只是重复了文章中引用的代码，(如上所述)是旧的CSS2(当您查看文章和这个答案首次发表的年份时，这是有意义的)。不管怎样，这里是有效的CSS3代码，方便您的复制和粘贴:

@media print {
    body{
        width: 21cm;
        height: 29.7cm;
        margin: 30mm 45mm 30mm 45mm; 
        /* change the margins as you want them to be. */
   } 
}

如果你认为你真的需要像素(你应该避免使用像素)，你必须注意选择正确的打印DPI:

72 dpi (web) = 595 X 842像素 300 dpi(打印)= 2480 X 3508像素 600 dpi(高质量打印)= 4960 X 7016像素

但是，我会避免这种麻烦，简单地使用cm(厘米)或mm(毫米)来确定大小，因为这样可以避免根据您使用的客户机而产生的渲染故障。