Print size planner
Runs in your browser. Nothing you type is sent or saved. Use the resolution your printer or lab asks for.
How does the planner work?
- Pixels needed = print width x pixels per inch, by print height x pixels per inch. Centimetres are converted at exactly 2.54 cm to the inch, the definition NIST gives (1 inch = 25.4 mm).
- Best output shape: for each Nano Banana model it picks the documented aspect ratio that crops the least from your print shape, then shows the 1K, 2K and 4K sizes Google lists for that ratio.
- GPT Image custom size: it searches every size OpenAI's rules allow (width and height multiples of 16, long side at most 3 times the short side, no edge over 3,840 pixels, 655,360 to 8,294,400 pixels in total) and keeps the one that gives the most pixels per inch at your print size. OpenAI calls sizes above 2560 x 1440 experimental.
- Pixels per inch at your size = the smaller of output width / print width and output height / print height. The image is scaled to cover the print and the overhang is cropped.
- Cropped away = 1 - (pixels inside the print area / all output pixels).
- Upscale needed = target ppi / pixels per inch at your size, when that is above 1.
Which sizes do the models output?
Pixel sizes from Google's Gemini API image generation docs for Nano Banana 2.1 (gemini-nano-banana-2.1). Nano Banana Pro (gemini-3-pro-image) lists the same sizes for 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9 and 21:9. Nano Banana 2.1 also adds 1:4, 4:1, 1:8 and 8:1.
| Aspect ratio | 1K | 2K | 4K |
|---|---|---|---|
| 1:1 | 1024 x 1024 | 2048 x 2048 | 4096 x 4096 |
| 2:3 | 848 x 1264 | 1696 x 2528 | 3392 x 5056 |
| 3:2 | 1264 x 848 | 2528 x 1696 | 5056 x 3392 |
| 3:4 | 896 x 1200 | 1792 x 2400 | 3584 x 4800 |
| 4:3 | 1200 x 896 | 2400 x 1792 | 4800 x 3584 |
| 4:5 | 928 x 1152 | 1856 x 2304 | 3712 x 4608 |
| 5:4 | 1152 x 928 | 2304 x 1856 | 4608 x 3712 |
| 9:16 | 768 x 1376 | 1536 x 2752 | 3072 x 5504 |
| 16:9 | 1376 x 768 | 2752 x 1536 | 5504 x 3072 |
| 21:9 | 1584 x 672 | 3168 x 1344 | 6336 x 2688 |
| 1:4 | 512 x 2048 | 1024 x 4096 | 2048 x 8192 |
| 4:1 | 2048 x 512 | 4096 x 1024 | 8192 x 2048 |
| 1:8 | 384 x 3072 | 768 x 6144 | 1536 x 12288 |
| 8:1 | 3072 x 384 | 6144 x 768 | 12288 x 1536 |
Google says the Gemini 3 image models generate 1K by default. OpenAI's image guide recommends 1024 x 1024, 1536 x 1024 and 1024 x 1536 for its current GPT Image models, and allows custom sizes within the rules above.
How big can common prints go?
Computed with the planner at 300 pixels per inch. "Nano Banana 2.1, 4K" uses the least-cropping ratio; "GPT Image, largest custom" uses the best size the rules allow.
| Pixels needed at 300 ppi | Nano Banana 2.1, 4K | GPT Image, largest custom | |
|---|---|---|---|
| 4 x 6 in | 1,200 x 1,800 | 2:3, 3392 x 5056: 843 ppi | 2352 x 3520: 587 ppi |
| 5 x 7 in | 1,500 x 2,100 | 3:4, 3584 x 4800: 686 ppi | 2432 x 3408: 486 ppi |
| 8 x 10 in | 2,400 x 3,000 | 4:5, 3712 x 4608: 461 ppi | 2576 x 3216: 322 ppi |
| 11 x 14 in | 3,300 x 4,200 | 4:5, 3712 x 4608: 329 ppi | 2544 x 3248: 231 ppi, upscale 1.30x |
| 16 x 20 in | 4,800 x 6,000 | 4:5, 3712 x 4608: 230 ppi, upscale 1.30x | 2576 x 3216: 161 ppi, upscale 1.87x |
| 18 x 24 in | 5,400 x 7,200 | 3:4, 3584 x 4800: 199 ppi, upscale 1.51x | 2496 x 3312: 138 ppi, upscale 2.17x |
| 24 x 36 in | 7,200 x 10,800 | 2:3, 3392 x 5056: 140 ppi, upscale 2.14x | 2352 x 3520: 98 ppi, upscale 3.07x |
| A4, 21 x 29.7 cm | 2,480 x 3,508 | 2:3, 3392 x 5056: 410 ppi | 2416 x 3424: 292 ppi, upscale 1.03x |
| A3, 29.7 x 42 cm | 3,508 x 4,961 | 2:3, 3392 x 5056: 290 ppi, upscale 1.03x | 2416 x 3424: 207 ppi, upscale 1.45x |
Upscaling enlarges the pixels the model produced. Check any upscaled file at full size before it goes to the lab, and look for the uneven detail described on the signature page.
Sources
Checked 13 November 2026:
- Google AI for Developers: Nano Banana image generation, Gemini API (aspect ratios and image size tables)
- OpenAI: Image generation guide (size and quality options, custom size rules)
- NIST: SI units, length (definition of the inch)