| 4 × 6 in | 10.2 × 15.2 cm | 600 × 900 | 1200 × 1800 |
| 5 × 7 in | 12.7 × 17.8 cm | 750 × 1050 | 1500 × 2100 |
| 8 × 10 in | 20.3 × 25.4 cm | 1200 × 1500 | 2400 × 3000 |
| 11 × 14 in | 27.9 × 35.6 cm | 1650 × 2100 | 3300 × 4200 |
| 16 × 20 in | 40.6 × 50.8 cm | 2400 × 3000 | 4800 × 6000 |
| 18 × 24 in | 45.7 × 61.0 cm | 2700 × 3600 | 5400 × 7200 |
| 24 × 36 in | 61.0 × 91.4 cm | 3600 × 5400 | 7200 × 10800 |
| A4 · 8.27 × 11.69 in | 21.0 × 29.7 cm | 1240 × 1754 | 2480 × 3508 |
| A3 · 11.69 × 16.54 in | 29.7 × 42.0 cm | 1754 × 2480 | 3508 × 4961 |
| A2 · 16.54 × 23.39 in | 42.0 × 59.4 cm | 2480 × 3508 | 4961 × 7016 |
| A1 · 23.39 × 33.11 in | 59.4 × 84.1 cm | 3508 × 4967 | 7016 × 9933 |
One formula, solved in any direction
DPI means dots per inch: the number of printer dots your file dedicates to every inch of paper. The math behind this calculator is a single multiplication — pixels equal inches times DPI, independently for width and height — but the three quantities can be entered in any order, which is exactly what makes the page useful. Type the pixel dimensions exported from your camera, scanner or image editor, type the physical print in inches or centimetres, and enter a resolution; as soon as any two of the three groups are complete, the missing group is solved instantly and every linked field updates together. Editing an inch value rewrites the centimetre boxes using the exact 2.54 centimetres-per-inch conversion, and editing centimetres works in reverse the same way, so mixed-unit planning can never quietly disagree with itself.
The quick-size bar fills the physical fields for the formats people actually order — 4×6, 5×7, 8×10, 11×14, 16×20, 18×24 and 24×36 inches — alongside the metric A4, A3, A2 and A1 sheet sizes. Underneath the calculator, the full reference table lists every one of those formats in both inches and centimetres, with the exact pixel counts a print lab expects at 150 DPI and at 300 DPI. Treat it as a shopping list when you size an export: an 18×24 poster needs 2700×3600 pixels at 150 DPI for a quick proof and 5400×7200 pixels at 300 DPI for the crisp gallery print. Each number is rounded only once, at the very end, so the width and height of every row stay internally consistent.
A verdict and a keepsake card
The verdict bar reads the effective resolution of your current numbers: 300 DPI and above is sharp and print-ready, roughly 150 DPI is acceptable for posters viewed from a step or two away, and anything below 150 risks visible softness — green, gold and red make the reading immediate. The effective DPI always uses the weaker of the two axes, so a wide file cannot hide behind a tall one. On the right, the live result card collects your pixels, physical size and resolution into a composed poster with the verdict band and a short 150/300 pixel summary, and Download repaints that card from scratch at 300 DPI in the print size you select from the menu. Nothing ever leaves your browser: there is no upload, no account and no server request, only local arithmetic followed by one PNG.
一条公式，三个方向任意求解
DPI 是每英寸点数，也就是你的文件为纸张上每一英寸分配的打印点数量。这个计算器背后的数学只有一条乘法——像素等于英寸乘以 DPI，宽和高各自独立计算——但三个量可以按任意顺序填写，这正是本页好用的原因。输入相机、扫描仪或图像软件导出的像素尺寸，输入英寸或厘米的物理打印尺寸，再填一个分辨率；三组中任意两组填好，第三组就会立即算出，所有联动字段同时刷新。修改英寸时，厘米框会按精确的 1 英寸 = 2.54 厘米重写；修改厘米时也会反向换算，混合单位规划永远不会在后台悄悄不一致。
快捷尺寸栏会替你填入大家真正会冲洗的规格——4×6、5×7、8×10、11×14、16×20、18×24、24×36 英寸，以及公制的 A4、A3、A2、A1 纸张。计算器下方的完整对照表逐一列出这些规格的英寸与厘米尺寸，以及印厂在 150 DPI 与 300 DPI 下要求的精确像素数。导出文件时可以把它当作采购清单：一张 18×24 海报，150 DPI 的快速样稿需要 2700×3600 像素，而锐利的画廊级 300 DPI 成品需要 5400×7200 像素。每个数字只在最后一步四舍五入一次，因此每一行的宽高始终自洽。
质量判定与可留存的结果卡
判定条会解读当前数字的有效分辨率：300 DPI 及以上为锐利、可直接印刷；150 DPI 上下适合隔一两步观看的海报；低于 150 则有发虚风险——绿、金、红三色让结论一目了然。有效 DPI 永远取宽高两个方向中较弱的一个，因此横向像素不足无法藏在纵向数字后面。右侧的实时结果卡把你的像素、物理尺寸与分辨率汇集成一张排版海报，带上判定色带与 150/300 像素摘要；点击下载时，这张卡会按你在菜单中选择的印刷尺寸以 300 DPI 从零重绘。整个过程没有任何数据离开浏览器：不上传、不注册、不请求服务器，只有本地计算和一张 PNG。
What DPI should I use for a poster?
300 DPI is the safe standard for framed prints and gifts viewed up close. Large wall posters seen from across a room tolerate 150–200 DPI because the eye cannot separate the dots at that viewing distance. Size your export from the reference table and let the verdict bar confirm your numbers before you send anything to print.
海报应该用多少 DPI？
300 DPI 是装框印刷与近看礼物的稳妥标准；需要隔着房间观看的大型墙面海报，150–200 DPI 也可以接受，因为在那个观看距离下肉眼无法分辨网点。按对照表确定导出像素，发印前再让判定条确认一次数字即可。
Are DPI, PPI and resolution the same thing?
DPI strictly means printed dots per inch and PPI means image pixels per inch, but in everyday poster workflow the two numbers are used interchangeably. This calculator treats the file as pixels per inch; the print shop then maps those pixels onto dots, so matching the requested DPI keeps the print crisp.
DPI、PPI 和分辨率是一回事吗？
严格说 DPI 是每英寸打印点数，PPI 是每英寸图像像素数，但在日常海报流程里两者基本混用。本计算器把文件按每英寸像素处理，印厂再把这些像素映射为墨点；让文件 DPI 与印厂要求一致，印刷就会清晰。
Why did the calculator overwrite a field I had typed?
The three groups are a closed equation. Once two of them are filled, the third is mathematically determined, and when all three contain values the group you edited most recently is recalculated from the other two so the row can never contradict itself. Change any field and the dependent values follow immediately.
为什么计算器会改写我已经填过的输入框？
三组数字构成一个封闭方程：任意两组确定后，第三组在数学上即被唯一确定；三组都有值时，最近编辑的那一组会根据另外两组重算，整行数字因此永远不会自相矛盾。修改任意字段，相关数值都会立刻跟随。
