Points are a weird and inconsistent unit of measure
Points are a weird and inconsistent unit of measure
“点”（Points）是一个奇怪且不一致的度量单位
May 13, 2026. Where Webtech and LaTeX can’t agree. I’m in the middle of redoing the Logic for Programmers diagrams and this has surfaced a really annoying problem. The book is formatted in LaTeX using a pseudo-grid of 10.8pt × 7.2pt. The diagrams are done in Inkscape using a 10.8pt × 7.2pt. Last week I found out that these are not the same points. 2026年5月13日。Web技术与LaTeX无法达成共识。我正在重做《程序员逻辑》（Logic for Programmers）一书的图表，这引出了一个非常令人恼火的问题。这本书使用LaTeX排版，采用10.8pt × 7.2pt的伪网格；而图表是在Inkscape中制作的，同样使用10.8pt × 7.2pt。上周我发现，这两个“点”并不是同一个单位。
Latex defines a point as 1/72.27 inches (0.3515 millimeters). Inkscape instead uses 1/72 inches (0.3528 mm). It’s only a difference of 0.4% but it still floors me that two widespread digital technologies would be different! So, uh, what happened? A few hours of reading articles later, this is what I found, caveat that I didn’t spend all that much time researching this and this is only initial impressions. LaTeX将一个点定义为1/72.27英寸（0.3515毫米）。而Inkscape使用的是1/72英寸（0.3528毫米）。虽然只有0.4%的差异，但两种广泛使用的数字技术竟然存在这种不同，这依然让我感到震惊！那么，到底发生了什么？在阅读了几个小时的文章后，我有了以下发现。需要说明的是，我并没有花太多时间深入研究，这些仅是我的初步印象。
What even is a point?
到底什么是“点”？
A point is a typographic measure, coming from 1517, that is supposedly the smallest interesting size for a printer. This was notably not a standardized measure—different companies in times used different point sizes depending on their equipment. Over time it was standardized, but each country picked a different standard: the German and Japanese point is 0.250 mm, the French point is allegedly 0.399 mm, etc. But early computer history is super Americentric so that’s what technology uses. “点”是一种排版度量单位，起源于1517年，据说是印刷工眼中最小的有效尺寸。值得注意的是，这并不是一个标准化的度量——不同时期的不同公司根据其设备使用不同的点大小。随着时间的推移，它逐渐标准化，但每个国家选择了不同的标准：德国和日本的点是0.250毫米，法国的点据说是0.399毫米，等等。但早期的计算机历史非常以美国为中心，因此技术领域沿用了美国的标准。
In the US, they standardized the point around the end of the 19th century. To what? I dunno. This source from 1900 gives the length of a point as 35/996 cm (72.281 points/in) and then says there are exactly 867.4699 “ems per foot” (72.289 points/in). This source from 1916 says the standard pica (12 points) is 0.16604 inches and that there are 72.272 “pica ems per foot”. Which conveniently enough gives us 72.272 points/in (a pica being 12 points). Then on the very next page they say no a pica is actually 0.166044 inches and a point is exactly 0.013837 inches. I found other sources with other definitions, too. I’m going to chalk the differences up to a mix of “the definitions of ‘meter’ and ‘foot’ changed over time” and “these are less than a micron apart so who gives a shit”. I do, I give a shit. 在美国，他们在大约19世纪末标准化了“点”。标准是多少？我不知道。1900年的一份资料将点的长度定为35/996厘米（72.281点/英寸），并称每英尺有867.4699个“em”（72.289点/英寸）。1916年的一份资料称，标准的派卡（pica，12点）为0.16604英寸，每英尺有72.272个“派卡em”。这很方便地得出了72.272点/英寸（1派卡=12点）。然而在下一页，他们又说不，派卡实际上是0.166044英寸，一个点正好是0.013837英寸。我还发现了其他定义不同的来源。我将这些差异归结为“‘米’和‘英尺’的定义随时间而变”以及“这些差异不到一微米，谁在乎呢”。但我很在乎。
Regardless, the official NIST definition settled on a point being 0.013837 inches, so you’d get 72.27 points/inch. Wrong! You absolute moron. You get 72.270001 points/inch. This annoyed Donald Knuth enough that he rejiggered the ratio in TeX (pg 58): 无论如何，NIST（美国国家标准与技术研究院）的官方定义将点定为0.013837英寸，所以你会得到72.27点/英寸。错！你这个笨蛋。你会得到72.270001点/英寸。这让高德纳（Donald Knuth）非常恼火，以至于他在TeX中重新调整了这个比例（第58页）：
TEX’s “pt” has been made slightly larger than the official printer’s point, which was defined to equal exactly .013837 in by the American Typefounders Association in 1886 [cf. National Bureau of Standards Circular 570 (1956)]. In fact, one classical point is exactly .99999999 pt, so the “error” is essentially one part in 10^8. … The new definition 72.27 pt = 1 in is not only better for calculation, it is also easier to remember. TeX的“pt”被做得比官方印刷点稍大一些，后者由美国字体铸造协会在1886年定义为正好等于0.013837英寸[参见国家标准局第570号通告（1956）]。事实上，一个经典点正好是0.99999999 pt，所以这个“误差”本质上是10^8分之一。……新的定义72.27 pt = 1英寸不仅更利于计算，也更容易记忆。
(To explain his motivation a little: American printers measure things in inches, and define the point in terms of inches. TeX measures things in points, and define the inch in terms of points.) For the record, NIST seems to think “72 points/inch” is a good enough approximation. TeX calls this the bp (big point). （稍微解释一下他的动机：美国印刷商以英寸为单位测量事物，并根据英寸定义点。而TeX以点为单位测量事物，并根据点定义英寸。）顺便提一下，NIST似乎认为“72点/英寸”是一个足够好的近似值。TeX将其称为bp（大点）。
AKA the Inkscape value
也就是Inkscape的值
Now what about Inkscape? As far as I can tell, this comes from the Postscript format’s definition of the unit size: 那么Inkscape呢？据我所知，这源于PostScript格式对单位尺寸的定义：
The length of a unit along the x axis and along the y axis is 1/72 of an inch. We call this coordinate system default user space. … The unit size, 1/72 of an inch, is very close to the size of a printer’s point (1/72.27 inch), which is a standard measuring unit used in the printing industry. 沿x轴和y轴的单位长度为1/72英寸。我们将此坐标系称为默认用户空间。……单位尺寸1/72英寸非常接近印刷点的尺寸（1/72.27英寸），这是印刷行业使用的标准度量单位。
Later on page 86 they straight up call 1/72 inch a “point”. Later editions would clarify it’s not actually a point and that points are stupid anyway: 在第86页，他们直接将1/72英寸称为“点”。后来的版本澄清说它实际上并不是一个点，而且“点”本身就很愚蠢：
Note: The default unit size (1/72 inch) is approximately the same as a “point,” a unit widely used in the printing industry. It is not exactly the same as a point, however; there is no universal definition of a point. 注：默认单位尺寸（1/72英寸）与印刷行业广泛使用的“点”大致相同。然而，它并不完全等同于点；因为点没有统一的定义。
Apple shipped PostScript in their LaserWriter laser printer, other companies followed suite, making PostScript the de facto printing language and 72 points/in the standard digital measure. The W3 consortium used the same measure in CSS and SVG, Inkscape is an SVG editor, and that’s all she wrote. 苹果公司在其LaserWriter激光打印机中搭载了PostScript，其他公司纷纷效仿，使得PostScript成为事实上的打印语言，而72点/英寸成为了标准的数字度量单位。W3C联盟在CSS和SVG中使用了相同的度量，而Inkscape是一个SVG编辑器，事情就是这样。
If you’re reading this on the web, you can subscribe here. Updates are once a week. My main website is here. My new book, Logic for Programmers, is now in early access! Get it here. 如果你是在网页上阅读此文，可以在此处订阅。每周更新一次。我的主网站在这里。我的新书《程序员逻辑》现已开启抢先体验！点击此处获取。