Aspect Calc

AI-assisted project. This codebase was created with Claude Code (Anthropic), directed and reviewed by a human author. The arithmetic is pinned by 100 tests, including the ratio-naming rules that are the only part with judgement in them — that 3440×1440 is reported as 21:9 rather than its exact reduction 43:18, and that 1366×768 is never called exactly 16:9 however close it lands. The PowerPoint sizing follows the format's own 56-inch slide limit. Nothing here has been checked by measuring a real screen, because there is nothing to measure: it is arithmetic over the numbers you type, and it is only as right as they are.

An aspect ratio, pixel pitch and display geometry calculator for people who put pictures on walls. Browser only — no account, no backend, nothing you type leaves the tab.

The whole model is one relation:

resolution (px)  ×  pixel pitch (mm)  =  physical size (mm)

Give it any two and it calculates the third. Diagonal and aspect ratio are two more ways of writing the physical size, so you can also hand it a 55" diagonal and "16:9" and get the width and height back.

What it does

• Aspect ratio from anything — a resolution in pixels, a physical size in mm/cm/m, inches or feet-and-inches, or a diagonal and a ratio.
• Names the ratio properly. 3440×1440 reduces exactly to 43:18, and nobody has ever ordered a 43:18 monitor — it is called 21:9. 1366×768 reduces to 683:384, which is not a ratio so much as an accusation; the useful answer is 16:9, 0.05% off. Both the trade name and the arithmetic are always shown, and a match that isn't exact says so and says by how much.
• Both decimal forms — 1.778 : 1 and 0.5625.
• Pixel pitch in any direction: pitch from resolution and size, size from resolution and pitch, or resolution from size and pitch. Non-square pixels are reported, not averaged away.
• Diagonal and area, always, in both measuring systems at once.
• PowerPoint slide sizes, both directions — the slide size for a target resolution, or the resolution a given slide size exports to. Handles the 56-inch cap, the 1-inch floor and the 100 MP export ceiling, and gives you points and EMU alongside inches and cm.
• The display drawn to scale with SMPTE-style colour bars and every dimension on it.

Running it

npm install
npm run dev

npm test          # 100 tests
npm run build     # tsc -b && vite build -> dist/

Notes from the trade

Pitch is centre-to-centre and every pixel owns a full cell, so physical width is horizontal pixels × pitch, not (pixels − 1) × pitch. A 168 × 168 px cabinet at 2.9 mm is 487.2 mm square, not 484.3. Getting this wrong loses one pitch across the whole wall, which is invisible in a spreadsheet and very visible when the last cabinet does not fit the frame.

The two 21:9s are not the same ratio. 2560×1080 is 64:27 (2.370:1) and 3440×1440 is 43:18 (2.389:1). They are 0.8% apart and both are sold as "21:9". The calculator names them both 21:9 and then tells you which one you have.

The colour bars are a picture, not a signal. The pattern is stretched to whatever aspect you are looking at — which is what a real generator does — and the RGB values are the standard 75% bar values but are not colour-managed. Do not grade against it.

Notes on PowerPoint

A slide is a display whose pixel pitch is fixed by the export DPI: slide size × DPI = pixels, and 96 dpi is a pitch of 0.265 mm. What makes it worth calculating is that PowerPoint adds three limits an LED wall does not have.

56 inches is a hard stop on either edge, and 1 inch is a hard floor. A 7680-wide wall at 96 dpi wants an 80-inch slide, which PowerPoint refuses. The answer is to build at half size and export at 200%, and the tool works out the divisor and the resulting export DPI for you. A shape steeper than 56:1 cannot be a PowerPoint slide at any scale, and it says so.

PowerPoint will not write a bitmap over 100 megapixels, so the export DPI has its own ceiling of sqrt(100,000,000 / (w × h)) with the slide in inches. On a 40 × 22.5 inch slide that is 333 dpi, whatever you put in ExportBitmapResolution.

PowerPoint's two 16:9 slide sizes are not the same size. "Widescreen" is 13.333 × 7.5 in; "On-screen Show (16:9)" is 10 × 5.625 in, which is also what Google Slides defaults to. Both are exactly 16:9, and a deck moved between them has every point size on every slide wrong by a third. This is why the tool always reports a size and never just a ratio.

Usually you should not resize the deck at all. For a 16:9 target the better answer is to leave the deck on Widescreen and raise the export DPI — 3840 px wide is just 288 dpi — which keeps every template, master and font size where it is. The tool offers that route whenever the ratio matches and the required DPI is a whole number, and withholds it when it is not, because ExportBitmapResolution is a DWORD and a rounded 102 dpi quietly delivers the wrong pixel count.

The dialog rounds, the file does not. Widescreen is 40/3 inches — 12,192,000 EMU — and the "13.333" the dialog shows is a genuinely different slide at 12,191,695 EMU. The presets here carry the exact values.

This project is built on other people's work — see ATTRIBUTIONS.md.

Licence

MIT. Part of Stoatworks Labs.