Star Map Poster Sizes, and How to Print One at Home
Pick the frame first, then the size menu: every print preset is a real page size, and each one downloads at a fixed, known number of pixels. No frame and no print shop? The same poster comes out of an ordinary printer on A4 or US Letter sheets that you trim and tape.
Design my poster
Free, no account, nothing to buy. Opens at 50 × 70 cm; the size menu has every preset below, and Print at home is under More formats & sharing.
Every print size, in pixels and in sheets
| Size | PNG at 300 dpi (px) | A4 sheets | Letter sheets |
|---|---|---|---|
| A3 | 3,508 × 4,961 | 4 (2 × 2) | 4 (2 × 2) |
| 30 × 40 cm | 3,543 × 4,724 | 4 (2 × 2) | 4 (2 × 2) |
| 40 × 50 cm | 4,724 × 5,906 | 6 (3 × 2) | 9 (3 × 3) |
| 50 × 70 cm | 5,906 × 8,268 | 9 (3 × 3) | 9 (3 × 3) |
| 60 × 90 cm | 7,087 × 10,630 | 16 (4 × 4) | 16 (4 × 4) |
| 70 × 100 cm | 8,268 × 11,811 | 16 (4 × 4) | 20 (4 × 5) |
| 11 × 14 in | 3,300 × 4,200 | 4 (2 × 2) | 4 (2 × 2) |
| 16 × 20 in | 4,800 × 6,000 | 6 (3 × 2) | 9 (3 × 3) |
| 18 × 24 in | 5,400 × 7,200 | 9 (3 × 3) | 9 (3 × 3) |
| 24 × 36 in | 7,200 × 10,800 | 16 (4 × 4) | 16 (4 × 4) |
The PNG and JPEG are the page size at 300 dpi; the PDF is a page of exactly that size with the same picture in it; the SVG is vector and has no pixel size at all. The sheet counts are what Print at home writes for that preset, columns × rows. Smaller presets (photo and card sizes from 4×6 in to A5, and six screen formats) are in the same menu.
Printing at home on A4 or Letter
Under More formats & sharing, Print at home on A4 / Letter sheets takes the very PDF that Download PDF writes and cuts it across ordinary sheets. Nothing is re-rendered or resampled: each sheet shows its part of the 300 dpi poster, so a sheet printed at 100 % is as sharp as the whole poster printed by a shop.
- Every sheet keeps a 12.7 mm margin, because home printers cannot ink the edge of the paper.
- Neighbouring sheets repeat the same 10 mm of the poster, so a sheet that prints a millimetre off, or a wobbly cut, still meets its neighbour with no white gap.
- Page 1 is an assembly sheet: the count, a small map of the poster with the grid and labels, the steps, and a 10 cm bar. Measure the bar; if it is not 10 cm, the printer scaled the pages, so print again at “Actual size”.
- Inch sizes default to US Letter sheets and metric ones to A4; the Sheet menu beside the button switches.
Lay the sheets out by their labels (A1 top left, row letters downwards), trim one edge of each overlap, line up the stars, and tape from behind.
Two honest limits
The PDF and the tiles come only at the preset sizes. For a size that is not in the menu, send the SVG: vector art scales without a limit. And the raster files are built in your browser’s memory: 50 × 70 cm is a nearly 49-megapixel canvas, which desktops handle but some phones refuse (iOS Safari caps a canvas at about 16.8 megapixels). Over that cap the page builds the file in strips, which works on most phones but not every one; 70 × 100 cm, at 97.7 megapixels, is always built in strips. If a phone still fails, take the SVG or make the poster again on a laptop.
What the chart draws
The chart holds the 1,630 stars brighter than magnitude 5.0 and the 89 constellation figures, and the Milky Way is drawn as a soft band. The Moon is drawn in its real phase, and left off when it was below your horizon. The five naked-eye planets, Mercury, Venus, Mars, Jupiter and Saturn, are drawn where they stood. The Sun is drawn too whenever it was up, and the caption says whether your moment was daylight, twilight or full dark: the stars are always drawn where they stood, even when daylight or twilight hid them. So is an eclipse, if your moment falls inside one. Uranus, Neptune and 133 deep-sky objects are one switch away: tick Deep-sky objects and the chart marks the Messier objects and southern showpieces and adds Uranus and Neptune (see them over London on a winter evening). Great comets since 1900 can be added (Hale-Bopp over London, 1997). Not drawn: faint comets and satellites, whose orbits this tool does not compute. Every position is carried to your date by precession. Not modelled: the stars’ own proper motion. A date before 15 October 1582 is read in the Julian calendar. It all runs in your browser, nothing is uploaded, and the downloads are complete and free. Accuracy, print sizes and privacy, answered in full.
Common questions
What file should I take to the print shop?
If the upload form asks for paper dimensions, the PDF: it is a page of exactly the size you picked with the 300 dpi poster placed in it, so the size is read from the file. If it asks for pixels, the PNG (5906 × 8268 px at 50×70 cm), or the JPEG if it refuses PNG. If it takes SVG, that is the best of all: vector art has no resolution to run out of.
Will the taped seams show?
Faintly, as thin lines where two sheets meet; the 10 mm overlap means there is never a gap. On the ink theme, mostly paper, they are hardest to see. Behind glass in a frame they almost vanish.
Can I make a landscape poster?
Not as a print: every print preset is portrait, the way star map posters are framed. The landscape sizes are the desktop wallpapers (2560×1440 and 3840×2160 px), which are screen formats and download as PNG.