Ordering a stamp is easy. Ordering the right-sized stamp is where people get stuck—because the difference between a 38 mm and a 45 mm seal sounds trivial until it is printed on a contract, dropped onto a notary acknowledgment, or handed to an engraver who needs exact dimensions in millimeters.
Most guides list sizes as a wall of numbers with no explanation of what any of them are for. This one gives you the full reference—round, rectangular, and oval standards, the real millimeter-to-pixel math, and how to set each dimension precisely in our free Stamp Studio—so the mark you design looks correct on screen, in print, and on a physical rubber stamp.
Reference, not a rulebook: These are industry conventions, not legal requirements. Where a statute, a court, or a platform mandates a specific size—notary seals are the common example—that requirement always wins. Our notary seal compliance guide covers the state-by-state specifics.
Why Proper Stamp Sizing Matters for Digital Documents and Physical Printing
A stamp has to survive two environments that pull in opposite directions: a screen and a sheet of paper.
On screen, size is forgiving. A stamp scaled to fit looks fine at any dimensions, and most people stop there. The problems begin when the same file reaches paper or a manufacturer. A mark designed at screen-pixel dimensions has no inherent physical size, so the printer, the PDF viewer, and the Word document each decide how large it should be—and they rarely agree. The result is a seal that dominates a signature block on one machine and shrinks to a smudge on another.
Setting the dimensions in real-world units solves this. When a stamp knows it is 40 mm across, a 300 DPI export, a document placement, and a physical order all describe the same object. Getting sizing right is the difference between a mark that reads as a genuine applied stamp and one that reads as a pasted image.
Three numbers govern every stamp:
- Diameter or width (mm) — the physical footprint, which determines how the mark relates to a signature line, a page margin, and other text.
- Resolution (DPI) — how many pixels represent each inch, which determines sharpness when scaled or printed.
- Aspect ratio — the width-to-height relationship of rectangular stamps, which must suit the text or lines the stamp carries.
Get these right and everything downstream—document placement, print quality, engraving—falls into place.
Circular Stamp Standards (38mm, 40mm, 42mm, 45mm, 50mm)
Round stamps dominate official and verification use because a circle reads as authoritative and its ring border naturally frames curved text. Five diameters cover nearly every real-world need.
| Diameter (mm) | Diameter (in) | Typical Use | Document Standard |
|---|---|---|---|
| 38 mm | 1.50 in | Notary public, doctor and professional certification marks | Standard Compact |
| 40 mm | 1.57 in | Corporate LLC seals, legal jurats, small business seals | Standard Legal |
| 42 mm | 1.65 in | Commonwealth notary, bank and financial verification | Commonwealth Standard |
| 45 mm | 1.77 in | Government agencies, academic diplomas, university seals | Government / Academic |
| 50 mm | 1.97 in | Large heritage crests, award badges, official emblems | Executive Crest |
Pro Tip: 40 mm is the safest default for a corporate seal. It is large enough to hold a company name, a state of incorporation, and a founding year legibly, yet small enough to sit beside a signature line without crowding the page. Start there and only move up if the entity name is unusually long.
The diameter is not the whole story for a round stamp—the usable text area shrinks with every ring you add. A 40 mm seal with three concentric borders has noticeably less room for text than the same stamp with a single outer ring. When a long company name will not fit, the fix is usually to widen the diameter or reduce the number of rings, not to shrink the type until it is illegible. Our step-by-step guide on how to create a digital stamp online walks through ring configuration and type fitting.
Rectangular & Square Stamp Standards (20x50mm, 25x65mm, 38x75mm)
Rectangular stamps carry the marks that read as actions rather than authority: APPROVED, PAID, RECEIVED, VOID, address blocks, and multi-line endorsements. Their width comes from the need to fit a word or a name on one line; their height comes from how many lines they must stack.
| Dimensions (mm) | Dimensions (in) | Typical Use | Aspect Ratio |
|---|---|---|---|
| 20 × 50 mm | 0.79 × 1.97 in | Single-line status stamps, small PAID / REVIEWED marks | 2.5 : 1 |
| 25 × 65 mm | 0.98 × 2.56 in | Multi-line address blocks, prescription and reference stamps | 2.6 : 1 |
| 38 × 75 mm | 1.50 × 2.95 in | Large endorsements, terms-and-conditions or certification blocks | 2.0 : 1 |
| 38 × 38 mm | 1.50 × 1.50 in | Square approval badges, QR or seal combinations | 1 : 1 |
| 50 × 30 mm | 1.97 × 1.18 in | Status box with a date line and signature line | 1.67 : 1 |
The order always reads “width × height.” A stamp that carries a date line, an approver initial line, and a status word needs the taller 50 × 30 mm or 38 × 75 mm formats; a stamp that carries a single word is better at 20 × 50 mm, where the footprint stays proportionate to its content.
Pro Tip: Match the aspect ratio to the longest line the stamp must hold. For a typical status stamp the magic number is roughly 2.5 : 1—wide enough for a word like
CONFIDENTIALat a readable size, short enough that the mark does not look like a label. Our APPROVED, PAID & RECEIVED stamp guide shows the format in a real accounts-payable workflow.
Oval Notary & Medical Seal Standards
Not every official stamp is round. Oval and elongated seals are required or preferred in specific professional contexts.
- Oval notary seals — Traditional in many US states and Commonwealth jurisdictions. Common formats are 25 × 64 mm (1 × 2.5 in), 30 × 45 mm (1.18 × 1.77 in), and 38 × 64 mm (1.5 × 2.5 in). The oval gives more horizontal room for a name, commission number, and county than a compact circle of the same area.
- Medical and prescription stamps — Almost always rectangular or elongated, typically 25 × 65 mm, to hold a physician name, credentials, license number, DEA number, and a clinic line in a stack of short lines. Our medical stamp guidelines cover the required elements.
- Bank and financial verification — Frequently oval or rectangular, sized to include a routing number, branch code, teller code, and transaction date without crowding.
Oval geometry is the reason curved-text tools matter: an oval carries text along two arcs of different radii, so top and bottom text must be calibrated independently. The Stamp Studio handles that automatically when you choose an oval geometry, keeping the bottom arc upright rather than inverted.
Resolution Calibration: Converting Millimeters to Pixels
Resolution and physical size are two separate decisions, and mixing them up is the single most common sizing mistake. A stamp is defined physically in millimeters; its pixel count is what changes with DPI.
The conversion is direct:
pixels = (millimeters ÷ 25.4) × DPI
So a 40 mm stamp is 40 ÷ 25.4 = 1.575 inches wide. Multiply that by the DPI and you have your pixel dimensions.
72 DPI (Web Screen Preview)
Screen resolution exists only to make the stamp look right online. At 72 DPI a 40 mm stamp is about 113 pixels across—enough for a thumbnail, far too little for anything that will be printed or stamped into a document. Never export a working stamp at screen resolution; it is a preview standard, not a delivery standard.
300 DPI (Standard Office Laser Printing)
300 DPI is the industry baseline for ordinary laser printing. At 300 DPI:
| Size | Pixel Dimensions at 300 DPI |
|---|---|
| 38 mm | ≈ 449 px |
| 40 mm | ≈ 472 px |
| 42 mm | ≈ 496 px |
| 45 mm | ≈ 531 px |
| 50 mm | ≈ 591 px |
A 300 DPI stamp is crisp at its true physical size on a normal office printer. It only breaks down when someone enlarges it—on screen at high zoom, or blown up in a PDF layout. If your workflow never scales the mark, 300 DPI is sufficient and keeps file sizes small.
600 & 1200 DPI (Archival Legal Quality & Laser Engraving)
600 DPI doubles the linear pixel count; 1200 DPI doubles it again. At 1200 DPI:
| Size | Pixel Dimensions at 600 DPI | Pixel Dimensions at 1200 DPI |
|---|---|---|
| 38 mm | ≈ 898 px | ≈ 1795 px |
| 40 mm | ≈ 945 px | ≈ 1890 px |
| 42 mm | ≈ 992 px | ≈ 1984 px |
| 45 mm | ≈ 1063 px | ≈ 2126 px |
| 50 mm | ≈ 1181 px | ≈ 2362 px |
Reach for 1200 DPI in three situations: the document will be scanned or photocopied (each pass degrades a low-resolution mark further), the stamp will be enlarged in a layout or on a poster, or the file is destined for commercial printing. The cost is a larger file, which is now irrelevant—a 2000-pixel PNG is still tiny by modern standards.
Pro Tip: When in doubt, export at 1200 DPI and let the document scale it down. Downscaling is always clean; upscaling a low-resolution file is not. There is no quality penalty for exporting higher than you need.
For rectangular stamps the same math applies per axis. A 25 × 65 mm stamp at 1200 DPI is roughly 1181 × 3071 pixels. Work it out line by line—width and height convert independently.
Printable Sizing Calibration Sheet
The fastest way to trust your dimensions is to see them against a real page. Print the table below at 100% scale—never “fit to page”—and lay a physical stamp or a ruler against it to compare.
| Mark | True Physical Size | Fits Letter with 1 in Margin? | Fits A4 with 1 in Margin? |
|---|---|---|---|
| Standard compact seal | 38 mm (1.50 in) | Yes | Yes |
| Standard legal seal | 40 mm (1.57 in) | Yes | Yes |
| Commonwealth seal | 42 mm (1.65 in) | Yes | Yes |
| Executive crest | 50 mm (1.97 in) | Yes | Yes |
| Small status stamp | 20 × 50 mm | Yes | Yes |
| Address / Rx block | 25 × 65 mm | Yes | Yes |
| Large endorsement | 38 × 75 mm | Yes | Yes |
The margin math is worth internalizing. US Letter is 216 × 279 mm and A4 is 210 × 297 mm; a 1-inch (25.4 mm) margin leaves a content area of 165 × 229 mm on Letter and 159 × 246 mm on A4. Every standard size above fits inside that area with room to spare, which is why stamp sizing almost never runs into a page-margin problem—it runs into a readability problem instead.
Pro Tip: “Fit to page” scaling is the enemy of calibration. Print at 100%, measure the outer ring with a ruler, and confirm it matches the millimeter figure in this guide before you commit to a physical order.
Setting Exact Dimensions in the Stamp Studio
Calibration is only useful if you can act on it. Here is how the numbers above map to the design workflow in the free Stamp Studio:
- Choose the geometry — round, oval, rectangular, or square—matching the standard you selected above.
- Set the diameter or width and height in millimeters, not pixels. The studio treats the figure as a real physical dimension, so exports and document placement stay consistent.
- Add rings and text, checking that the longest line fits inside the innermost border with margin to spare.
- Adjust spacing, not type size, when text crowds a ring—reduce the gap between arcs before you shrink the letterforms.
- Export a transparent PNG at your target resolution (300 DPI for office use, 1200 DPI for print or scan), or an SVG if the file will go to a physical stamp maker.
- Place the stamp in your document with the PDF & Word Stamper, keeping the size in millimeters so the mark lands at true scale.
If you are building a corporate mark, our guide to the official company seal pairs well with this reference—it explains which elements belong in a seal so you can size the stamp to fit them. And for choosing between a vector and a raster export, the upcoming comparison of SVG, PNG, and PDF formats will settle the question.
Ready-made layouts already apply the correct geometry and roughly correct dimensions, so you can start from a template and fine-tune rather than build from scratch: browse the Status & Business templates for rectangular badges or the Notary & Legal gallery for round and oval seals.
Final Thoughts
Stamp sizing is not a matter of taste—it is a conversion problem with a small set of accepted answers. Pick the diameter or dimensions that match the job, set them in millimeters so every downstream tool agrees, and export at a resolution that survives the harshest environment the mark will face. A 40 mm seal at 1200 DPI will look correct on screen, on paper, and on a physical stamp; a screen-pixel stamp will fail at least one of the three.
Design the mark once in the Stamp Studio, then apply it at true scale to contracts, certificates, and invoices in the PDF & Word Stamper—with the dimensions right from the start.
Size It Right, Then Stamp It
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👉 Launch the Free Online Stamp Studio — 100% Free Forever, Zero Watermarks, Instant SVG & High-Resolution PNG Export.
Need to apply the finished mark to a document? Open the PDF & Word Stamper and place it at exact millimeter scale, or start from a pre-sized template.