Sticker Border Maker
Add a clean white outline around any transparent PNG. Tune the thickness, color and smoothness, then download a print-ready sticker. Everything runs in your browser — your file is never uploaded.
For live speed the preview may use a lower resolution — the download is always rendered at your image's full resolution.
Upload a transparent PNG to reveal the border controls.
A real 3-inch die-cut job, end to end
You are sending a 3 × 3 inch die-cut sticker to a print shop that wants 300 DPI, so your artwork is exported at 900 × 900 px. Load it here and the slider opens at its default 16 px — which sounds generous until you convert it: 16 ÷ 300 = 0.053 inch, or 1.35 mm. That is under the ~2 mm most shops ask for, and a border that thin can vanish on one side if the cutter drifts. Work backwards instead: 2 ÷ 25.4 × 300 = 23.62 px, so you nudge the slider to 24 px, which is 2.03 mm of white at this DPI.
Those 24 px change what happens under the hood. The dilation splits the growth into round(24 ÷ 2) = 12 passes of 2 px each rather than one big 24 px jump, and the default smoothness of 6 fires 8 + 6 × 3 = 26 angular samples per pass — 312 offset copies of your silhouette in total. Small steps are the whole point: a single large offset ring leaves flat facets on tight curves like lettering serifs, while 2 px at a time keeps the grown edge round. The canvas is padded by the thickness plus 2 px, so 900 + 26 + 26 = 952 px square.
For the printer's cut file that means the contour follows the outside of the white at a constant 2.03 mm from your artwork, and the spare 2 px (0.17 mm) of clear pixels around the whole thing guarantees the white never runs to the PNG's own edge — the cutter's trace always has real transparency to lock onto. Leave Include shadow in the exported PNG unticked for this file: switching it on adds a 55 px margin per side and ships a 1062 × 1062 px, 3.54-inch canvas, which is a lovely listing mockup and a cut file the shop will reject.
Five ways a sticker border goes wrong
- The white disappears along one edge of the finished sticker. The thickness slider is in pixels, and pixels only mean something once you know the file's DPI. The default 16 px is 1.35 mm on a 300 DPI file but only 0.68 mm at 600 DPI — well under the tolerance any cutter works to. Convert before you drag: millimetres ÷ 25.4 × DPI. Two millimetres is 24 px at 300 DPI and 47 px at 600. Note the ceiling this implies — the slider stops at 60 px, which on a 600 DPI file buys you 2.54 mm and no more, so very high-resolution artwork is better downsampled to 300 DPI before it comes in here.
- Curves look faceted, like a polygon pretending to be a circle. Smoothness controls how many directions the silhouette is grown in on each pass, and the formula is 8 + s × 3. Left at 1 that is only 11 angular samples, so the outline is effectively an 11-sided shape swept around your artwork and the flats show up on anything tightly curved — serifs, thin stems, small circles. The default 6 gives 26 samples and the maximum 10 gives 38. Raising it costs render time and nothing else, so on lettering there is no reason to sit below 6.
- The border traces a rectangle instead of your artwork. The silhouette is built from the alpha channel, so a JPEG — which has none — or a PNG that was flattened onto a white background gives the tool a solid opaque rectangle to grow, and it dutifully grows the rectangle. The amber warning under the drop zone fires for exactly this: it samples the alpha values and reports when it cannot find a single pixel below 250. If you see it, the fix is upstream — remove the background and re-export as PNG. Nothing in these controls can recover a silhouette that is not in the file.
- The outline is a soft halo rather than a crisp edge. This is the same mechanism working against you. Because the silhouette inherits the source alpha rather than thresholding it, artwork with feathered edges — a glow, a soft brush, a drop shadow baked in, an over-enthusiastic background removal — hands the tool semi-transparent pixels. Each dilation pass composites dozens of offset copies on top of each other, so those partial alphas accumulate into a wide, gradually fading fringe instead of a clean line. Harden the edge in your editor first, or accept that the cut contour will follow something fuzzy.
- The print shop rejects the file for being the wrong size. The drop shadow is a mockup feature and it changes the canvas. Its margin is derived from the sticker's own dimensions: blur is 2% of the shorter side (never below 6), offset is 70% of the blur, and the margin added on every side is blur × 2 + offset + 4. On a 2-inch 300 DPI sticker that a 24 px border has grown to 652 × 652 px, that works out at 13, 9 and a 39 px margin — a 730 × 730 px file, 2.43 inches instead of 2.17. Worse than the size, the shadow is soft grey pixels in the transparency the cutter needs to trace. Export the cut file with Include shadow in the exported PNG unticked, then tick it and download again if you want a listing image.
Frequently asked questions
What is a die-cut border?
A die-cut border is the solid outline — usually white — that hugs the shape of a sticker so the cutting machine has a clean edge to follow. Instead of a plain rectangle, the sticker is cut around your artwork with a small margin, giving that classic "peel-off" die-cut look. This tool grows your PNG's silhouette outward by the thickness you choose and fills it with a solid color to create that margin.
How thick should a sticker border be?
For most die-cut stickers a border of roughly 1/16" to 1/8" (about 2–4 mm) works well — that translates to around 18–48 px at 300 DPI. Thin borders (10–20 px) look modern and subtle; thicker borders (40–60 px) read as bold and are more forgiving for the cutting machine's tolerance. When in doubt, most print shops recommend at least ~2 mm so the white edge stays visible even if the cut drifts slightly. For standard sizes and the matching pixel counts, see our guide to die-cut sticker sizes, bleed and border.
Why do I need a transparent PNG?
The border is generated from your image's transparency — the tool traces the edge between the visible pixels and the transparent background, then expands it. If your file has a solid (non-transparent) background, there is no silhouette to follow, so the border just wraps the rectangular image edges instead of your artwork. Remove the background first and export as PNG for a true die-cut outline.
Is my image uploaded anywhere?
No. Your PNG is decoded straight from disk into an <img> and drawn onto an offscreen <canvas>; the 300-odd dilation draws, the colour fill and the final canvas.toBlob export all run against that canvas inside this tab. There is no upload endpoint in the code, and nothing is written to localStorage or IndexedDB either, so closing the tab is the entire cleanup. The page does serve Google ads, as every page here does, but the ad script is never handed your artwork.