The short answer
A fake IWC Portugieser Automatic 40 copies the 40 mm case size, so diameter alone tells you nothing. The differences that survive close inspection sit in three places: case thickness, dial printing, and movement finish. Check them in that order and you can sort a careful replica from a rough one in a few minutes. Replicas win on price alone; they lose on thickness, dial furniture, and serviceability.
Genuine specs to compare against
Most 40 mm replicas clone one of the steel references in the IW3583 family. Note the exact reference before you compare, because dial layout and hand finish change between them.
- Case diameter: 40.4 mm
- Case thickness: roughly 12.3 mm to 12.4 mm
- Lug width: 20 mm
- Movement: IWC caliber 82200, Pellaton winding, 60-hour power reserve
- Dial: small seconds at 6 o'clock, no date window
- Water resistance: 5 bar
What you need
- Digital caliper or micrometer
- 10x loupe
- Bright, angled light
- The reference number you are comparing to
How to compare, step by step
- Measure the case across the 9-to-3 line, bezel edge to bezel edge, and write the number down.
- Measure thickness from the center of the caseback to the top of the crystal.
- Measure the lug width where the strap meets the case.
- Examine the applied numerals under the loupe and check the bevels on each edge.
- Inspect the small seconds subdial and confirm the hand tip reaches the printed track.
- Look for a date window at 3 o'clock, which the 40 mm Portugieser does not have.
- Turn the watch over and study the rotor through the display back.
- Check the depth and sharpness of the engraving on the caseback ring.
- Wind and set the watch, then feel the crown for grit or looseness.
- Inspect the strap stitching, lining, and the signature on the buckle.
Where replicas fall short
Thickness and case profile
Replica cases run 0.5 mm to 1.5 mm thicker because the copied movement sits deeper than the 82200. The lugs also read flatter, and the polished flank loses the soft transition into the bezel.
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Dial printing and subdial
Genuine printing is thin and dense. Replica printing is heavier, and the railway track on the small seconds usually smears under magnification. Applied numerals show rounded edges instead of cut bevels.
Movement and finish
The genuine rotor is gold with deep engraving and circular graining. Replica rotors are plated brass with shallow lettering, and the bridges carry stamped decoration instead of real perlage. Timekeeping drifts, and no watchmaker will stock parts for it.
Strap and hardware
Genuine alligator straps have a signed buckle and clean edge paint. Replica straps use embossed leather with uneven stitching and unbranded hardware.
Legal and practical risk
Selling or distributing counterfeit watches in the United States is a federal offense under the Trademark Counterfeiting Act. U.S. Customs and Border Protection seizes counterfeit watches at import, and a personal-use purchase is not a defense. A replica also carries no warranty, no parts supply, and no resale value.
Bottom line
Measure the case first, then the dial, then the movement. Thickness and movement finish are the two checks a replica cannot pass. If you want the real proportions and a movement that can be serviced for decades, the genuine reference is the only version that delivers both.