Why map size matters for VTTs
A battle map that looks perfect in your editor can break when you import it into Roll20 or Foundry VTT. The grid might not align, the image might load slowly, or tokens might snap to the wrong cells. Getting the pixel dimensions right before you export saves time and frustration.
This guide covers the exact numbers for both platforms, plus tips for RPG Map Editor exports.
The golden ratio: pixels per cell
Every grid-based VTT divides your map image by the number of grid cells. If your image is 3500 px wide and you tell the VTT it has 25 columns, each cell is 140 px.
Recommended pixels per cell:
- 70 px — minimum viable; tokens look soft but files are small
- 100 px — decent quality, good for large maps (40+ cells wide)
- 140 px — best balance of quality and performance (recommended default)
- 200 px — high-res; ideal for Foundry VTT scenes with detailed stamps
Choose a value and stick with it for the whole map. Mismatched cell sizes cause alignment drift.
Roll20 specifics
Roll20 has a hard 10 MB file size limit for free users (25 MB for Plus/Pro). Keep your maps under these limits:
| Grid size | Cell px | Image px | Approx PNG size |
|---|---|---|---|
| 20 × 20 | 140 | 2800 × 2800 | 1–3 MB |
| 25 × 25 | 140 | 3500 × 3500 | 2–5 MB |
| 30 × 30 | 140 | 4200 × 4200 | 3–7 MB |
| 40 × 40 | 100 | 4000 × 4000 | 2–5 MB |
Import steps:
- Upload the PNG to your Roll20 game
- Drag it onto the map layer
- Set page size to match your grid (e.g., 25 × 25)
- Right-click → "Set Dimensions" if the grid drifts
For the full walkthrough, see our Roll20 export guide.
Foundry VTT specifics
Foundry is more flexible. It reads the image dimensions and lets you configure the grid in the Scene settings. There is no hard file size limit, but practical limits apply:
| Grid size | Cell px | Image px | Notes |
|---|---|---|---|
| 25 × 25 | 140 | 3500 × 3500 | Fast load, good detail |
| 25 × 25 | 200 | 5000 × 5000 | High-res, smooth on desktop |
| 40 × 40 | 140 | 5600 × 5600 | Large dungeon, acceptable |
| 50 × 50 | 140 | 7000 × 7000 | Slow on weak machines |
Import steps:
- Place the PNG in your Foundry data folder or upload via the file browser
- Create a new Scene, set the background image
- Set grid size to match your cell px (e.g., 140)
- Adjust padding and initial view as needed
For the full walkthrough, see our Foundry VTT export guide.
RPG Map Editor export settings
In RPG Map Editor, your grid settings directly control the output:
- Set cells wide and cells tall in the project settings
- Set pixels per cell (140 recommended)
- The export PNG will be exactly
cells × px_per_cellin each dimension - No scaling or resampling — what you see is what you export
This makes grid alignment much more predictable if you enter the same grid dimensions on both sides.
Common sizing mistakes
- Exporting at screen resolution instead of project resolution. Always use the "Export" button, not a screenshot.
- Letting the VTT auto-detect the grid. Auto-detection guesses wrong more often than it guesses right. Enter the numbers manually.
- Using non-square cells. Stick to square grids (same px in X and Y) unless you specifically need hex.
- Forgetting padding. If your map has a border or bleed area, account for those pixels when setting the VTT grid.
Quick reference
For a standard 25 × 25 encounter map:
- RPG Map Editor: 25 cells wide, 25 cells tall, 140 px per cell
- Export: 3500 × 3500 px PNG
- Roll20: Page size 25 × 25, grid enabled
- Foundry: Scene grid size 140, background image 3500 × 3500
Start with these numbers and adjust as you learn what works for your group.
Try it yourself
Open the editor and start painting your next battle map — free, in your browser.
