On many occasions, I’ve seen people ask about the Omega Speedmaster sizes. Usually in terms of the “will it fit” conundrum.

“42mm, that’s too big, I’ll go for the FOiS (First Omega in Space, a reinterpretation of the CK 2998 design) it’s smaller.”

Ummm, well, that’s not really correct. Let’s have a look at why is that so.

What if I told you, that 42mm is not necessarily 42mm in terms of fit?

You’d probably question that. “But the manufacturer said…”

Forget what the manufacturer said. The diameter doesn’t always determine how it’ll fit.

For that matter, the fit is determined by how the watch spans from one side of the wrist to the other, where the lug to lug size is what matters.

For example, a 43mm watch with hidden lugs, or a “lugless” design with the lugs being recesses in the main bloc of the case will obviously wear smaller than a 39-40mm with a lug to lug distance of 48-50mm.

Or smaller than a Longines Legend Diver, where the lug to lug distance is – with the diameter of 42mm not even suggesting that – a whopping 56mm, which is the same as in the 46mm IWC Big Pilot’s Watch, and a hair short of the 47mm Panerai reissues.

So, what is it like with the Omega Speedmasters?

In case of the Speedmasters, the diameter is hardly the thing to be concerned about, as Omega provides the diameter including the crown and pusher guards. That doesn’t have any influence on the lug to lug distance.

The bezel diameter is still 39.7mm, just as it was in all Speedmasters since the 2915-3.

The first Speedmasters, ref. 2915-1 and 2915-2 had a diameter of 38mm. With the 2915-3, this was increased due to the use of a new bezel type, one with an insert as we know it today, instead of the single-piece engraved bezel.

Lug to lug, the Pro measures 48mm. Some people will say “it’s too big, I’ll get the smaller FOiS.”

The fun part is, that the FOiS won’t cause the watch to have the tips of the lugs further from the edge of the wrist.

That’s because the straight lug cases, vintage and contemporary alike, have the same lug to lug distance of 48mm.

Ultimate guide to Omega Speedmaster sizes

Omega Speedmaster Pro on a 19 cm (7.5 inches) wrist

Weight distribution

Oddly enough, the apparently smaller FOiS might seem heavier – due to the lack of crown guards and a sapphire crystal (obviously, heavier than hesalite).

The centre of gravity sits slightly higher in the FOiS.

“So, which is bigger?”

In terms of the area occupied, the Pro. The wide lugs and the crown guard certainly make it look more bulky than it really is.

In terms of concerns about lug overhang, neither, they’re the same.

“What about the contemporary cal.9300 Speedmasters?”

Oh, that’s funny, because in this case, the diameters matter even less.

44.25mm will likely appall some, but the lug to lug is…50mm. Still less than a 42mm Longines Legend Diver with its 56mm though.

“Does it mean it will be comfortable, then?”

Not necessarily, as they have a high-dome crystal in the case back, making them top-heavy on smaller wrists.

Not to mention that the bulk of the case flies high above the wrist itself.

“But what if I get the Co-Axial cal. 9300 reinterpretation of the 2915?”

That won’t serve you any better than the 44.25mm ones.

No, it might not have the crown guards, but the lug to lug is still circa 50mm, and it still has that bulky crystal in the back.

And again, the weight distribution kicks in.

“But there has to be something that’s not top-heavy!”

There is. The Speedmaster “Racing”, first introduced at Baselworld 2017 – they trimmed the high-dome case back crystal.

Still, if the lug to lug you’re more comfortable with would be 48mm, go for the Pro.

“But I don’t like manually wound movements, I prefer automatic”

Well, there’s nothing I can do about that.

Get a Speedmaster Reduced, if you’re OK with a modular automatic.

Ultimate guide Omega Speedmaster sizes

Omega Speedmaster Reduced

“But it’s too small!”

Awww, knock it off!

“But I want a Speedmaster!”

Then go and try some of them on, I can’t make a choice for you!

Seriously. It’s best to take a walk, think, try them on, and not rely on the individual experiences of others in terms of how it wears.

It feels different for everyone. Just like with shoes – two people might have the same shoe size, but that doesn’t mean that the same shoe will fit them identically.