A practical starting point: a 375 × 525 mm poster fits four A4 portrait sheets with 10 mm margins and 5 mm overlap. The download has six PDF pages: one calibration, one assembly map and four poster sheets.
Start with the wall space, not the page count
Measure where the poster will go. Enter that width and height in the poster maker, in millimetres or inches. “Final size” fixes the assembled poster dimensions; it does not promise that every sheet is completely filled.
Use “Page grid” when you want a particular number of columns and rows. That mode derives the finished dimensions from the paper, margin and overlap. Changing the paper orientation can therefore change the poster size. The orientation comparison always compares paper use at the same currently displayed finished size.
Choose A4 or US Letter to match your tray
A4 measures 210 × 297 mm. US Letter measures 215.9 × 279.4 mm, or 8.5 × 11 inches. These formats are close, but they are not interchangeable when you need a poster at an exact size.
| Finished poster | A4 portrait | A4 landscape | Letter portrait | Letter landscape |
|---|---|---|---|---|
| 297 × 420 mm | 4 | 6 | 4 | 6 |
| 375 × 525 mm | 4 | 6 | 6 | 6 |
| 500 × 700 mm | 9 | 8 | 9 | 8 |
For the 500 × 700 mm example, turning the paper landscape saves one sheet. For the 375 × 525 mm example, A4 portrait uses fewer sheets. There is no orientation that is always best.
Why a tiny size change can add several sheets
With A4 portrait paper and 10 mm margins, each sheet contains up to 190 × 277 mm of image. A 5 mm overlap means the next column starts 185 mm to the right and the next row starts 272 mm lower.
Two columns cover 375 mm and two rows cover 549 mm. A 400 × 560 mm poster crosses both boundaries, so it requires three columns and three rows. Its bottom-right tile contains only 30 × 16 mm of image. That narrow tile is correct: the PDF preserves your requested finished size.
Schematic for understanding the final partial row and column; use the live preview for actual proportions.
Keep the image whole, or fill the poster
“Show whole image” preserves all of your picture and may leave white space if its proportions differ from the poster. “Fill poster” covers the entire poster but crops edges. Adjust the horizontal and vertical controls to keep the important part, and check both the whole poster and the individual-sheet preview.
Enlarging an image cannot restore missing detail. The effective DPI readout uses the working image and its placed size, including zoom. Below 100 DPI, expect visible pixels; 100–149 DPI may look soft up close. A larger original or a smaller poster is the practical fix. The tool uses a bounded working image to control memory and reports that reduction.
Print one test, then assemble
- Generate the PDF. Confirm the paper and Actual size setting. Print PDF page 1 first; its 100 mm and 2 inch lines should measure correctly.
- Print the poster pages. Use single-sided printing and the same paper, orientation and 100% scale. The poster begins on PDF page 3. See the calibration troubleshooting guide if the test is off.
- Follow the map. Trim white edges at the marks. Place each right or lower sheet over its neighbour's repeated strip, align the picture and tape the back. With zero overlap, butt the image edges together.
Questions before you use the paper
Can I print an A3-size picture on two A4 sheets?
Not at exact A3 dimensions with these default margins. A 297 × 420 mm picture uses four A4 portrait sheets in the table above. Printer-safe margins reduce the usable area, and overlap repeats part of the image. Choose a smaller finished size if two sheets are the priority.
Do all sheets have to be printed in one session?
No. Save the PDF and the local project first. You can print selected poster pages later using the same paper and scale. Use the map's sheet labels and PDF page numbers; do not accidentally print the calibration or map as a poster tile.
Does FirstPrint accept PDFs or order physical prints?
No. It accepts still JPG, PNG and WebP images, up to 12 MiB, 16 MP and 8,192 pixels per side. It creates a local PDF; it does not split an existing PDF, order printing or deliver a physical poster.
Check your own picture.
Open the studio, choose your image and inspect the finished size before you download.
Open the poster maker →Basis and limits. These examples come from FirstPrint's checked geometry and real generated PDFs. An independent PDF parser verified page dimensions, image placement and matching overlap pixels. Physical printing has not yet been verified. Printer margins and colour output vary.
For further background on home poster printing and Actual size, see the Rasterbator FAQ. Local processing, trim marks and calibration are established features, not exclusive FirstPrint claims. Read our credits and licenses.