28.5mm vs 30.8mm Seiko Dials: Which Size Do You Need? (2026)

Choosing the wrong dial size is the most common mistake in Seiko modding — and the most frustrating. A 30.8mm dial won't fit a 28.5mm case, and forcing it risks damaging both the dial and the movement. This guide breaks down exactly which size you need, which cases accept which dials, and how to avoid expensive mistakes.

Quick Answer: Which Size Do You Need?

• Building with an SKX007 case, Royal Oak 37mm, Petrichor 37mm, or most 36-39mm mod cases? → You need 28.5mm dials
• Building with a Seikonaut/Nautilus 40mm, Royal Oak 41mm, Turtle, Sumo, or Samurai case? → You need 30.8mm dials

When in doubt, check the case listing — every case on our store specifies dial compatibility.

What Are Seiko Mod Dial Sizes?

Seiko uses two standard dial sizes across nearly all their NH-movement watches. These same standards carry over to the aftermarket modding world:

• 28.5mm — the smaller standard, used in SKX007/009, SRPD, SNK, and most compact mod cases
• 30.8mm — the larger standard, used in Sumo, Turtle, Samurai, and larger mod cases like the Seikonaut 40mm and Royal Oak 41mm

These aren't arbitrary numbers — they correspond to the movement holder and case interior dimensions. The dial feet (small pins on the back of the dial) must align with the movement's dial feet holes, and the outer edge must sit flush against the chapter ring or case interior.

How Dial Sizes Are Measured

Dial size refers to the outer diameter of the dial disc, measured in millimeters. This is not the same as the visible dial area (which is smaller due to the chapter ring overlap) or the case diameter (which is measured at the bezel).

• 28.5mm dial = 28.5mm outer diameter, approximately 27mm visible area
• 30.8mm dial = 30.8mm outer diameter, approximately 29mm visible area

The difference is only 2.3mm in diameter — but that's enough to make them completely non-interchangeable without modification.

28.5mm Dial: Specs & Compatible Cases

Technical Specifications

Spec	Detail
Outer Diameter	28.5mm
Feet Position	Standard NH35/4R position
Compatible Movements	NH35, NH36, NH38, NH70, NH71, NH72, 4R35, 4R36
Date Window	At 3 o'clock (NH35/NH36) or no date (NH38/NH72)

Compatible Nomods Cases

• Royal Oak 37mm V2 ($149) — all 5 colors
• Petrichor 37mm ($195) — all 5 colors

Compatible Seiko Models (OEM)

• SKX007 / SKX009 / SKX011
• SRPD series (5KX)
• SNK803 / SNK805 / SNK809
• SNZF15 / SNZF17 (Sea Urchin)

30.8mm Dial: Specs & Compatible Cases

Technical Specifications

Spec	Detail
Outer Diameter	30.8mm
Feet Position	Standard NH35/4R position (same as 28.5mm)
Compatible Movements	NH35, NH36, NH38, NH70, NH71, NH72, 4R35, 4R36
Date Window	At 3 o'clock (NH35/NH36) or no date (NH38/NH72)

Compatible Nomods Cases

• Seikonaut 40mm ($149) — all 6 colors
• Royal Oak 41mm ($110) — all 4 colors

Compatible Seiko Models (OEM)

• SRP Turtle series (SRPE, SRPC)
• SBDC Sumo series
• SRPB Samurai series

Direct Comparison Table

Feature	28.5mm	30.8mm
Outer Diameter	28.5mm	30.8mm
Visible Area	~27mm	~29mm
Best Case Sizes	36-39mm	40-44mm
Movement Compatibility	All NH/4R	All NH/4R
Aftermarket Selection	Largest (hundreds of options)	Good (fewer than 28.5mm)
Price Range (Nomods)	$29–$40	$32–$40
Typical Case Diameter	37-39mm	40-44mm

Case Compatibility Matrix

Nomods Case	Dial Size	Price
Royal Oak 37mm V2	28.5mm	$149
Petrichor 37mm	28.5mm	$195
Seikonaut 40mm	30.8mm	$149
Royal Oak 41mm	30.8mm	$110

Visual Impact: Same Dial, Different Cases

The dial-to-case ratio dramatically affects how a watch looks on your wrist:

• 28.5mm dial in a 37mm case — the dial fills about 77% of the case diameter. This creates a balanced, classic look with visible chapter ring detail.
• 30.8mm dial in a 41mm case — the dial fills about 75% of the case diameter. Similar proportions, but the larger overall size makes more visual impact.
• 28.5mm dial in a 42mm+ SKX case — the dial only fills 68% of the case. More chapter ring is visible, which can look either sporty or slightly undersized depending on the dial design.

If you want maximum dial presence, match the recommended size: 28.5mm for compact cases, 30.8mm for larger cases.

Aftermarket Availability

28.5mm Dials at Nomods

• Royal Oak Skeleton V1 28.5mm — Silver, Gold, Rose Gold ($40)
• Royal Oak Skeleton V2 28.5mm — Silver, Gold, Rose Gold ($40)
• Waffle Dial 28.5mm — Blue, Green, Gray, Tiffany, Black ($29)
• Sunburst Sector Dial 28.5mm — Blue, Black, Green ($39)
• Skeleton Dial 28.5mm — Green ($39)

30.8mm Dials at Nomods

• Nautilus Dial 30.8mm — Blue, Green, Chocolate ($32)
• Nautilus Dial Gray ($32)
• Nautilus Skeleton Dial 30.8mm — Black, Golden, Royal Blue, Army Green ($32)
• Nautilus Skeleton Dial 30.8mm Index — Gold, Silver, Rose Gold, Black PVD ($40)
• Royal Oak Skeleton Dial 30.8mm — Silver, Gold, Rose Gold ($39)

Browse the full selection in our Seiko Mod Dials collection.

Installation Tips for Each Size

General Rules (Both Sizes)

1. Work in a clean, dust-free environment
2. Use a dust blower before placing the dial
3. Align the dial feet with the movement holes — never force them
4. Check date window alignment before pressing the dial fully home
5. Use a loupe to verify the dial is perfectly centered

28.5mm Specific

These dials are standard across the widest range of cases and movements. Installation is straightforward — the dial feet snap into the movement's receiving holes. If using aftermarket dials with different feet positions, you may need to trim the feet and use dial dots (adhesive pads) instead.

30.8mm Specific

Larger dials require more careful alignment because any miscentering is more visible on the larger surface. Take extra care with the chapter ring placement — on 30.8mm builds, the chapter ring gap between dial edge and case interior is tighter.

Can You Use Adapters?

Technically, you can fit a 28.5mm dial into a 30.8mm case using a spacer ring — but we don't recommend it for most builds:

• Pros: Access to the wider 28.5mm aftermarket selection in larger cases
• Cons: Visible gap around the dial edge, chapter ring mismatch, looks unfinished

Going the other direction (30.8mm into a 28.5mm case) is physically impossible — the dial simply won't fit.

For the best results, always use the correct dial size for your case. If you want a specific dial design that's only available in 28.5mm, consider building with the Royal Oak 37mm or Petrichor 37mm instead.

Which Size Should You Choose?

Choose 28.5mm if:

• You're building with a 37mm case (Royal Oak 37mm or Petrichor)
• You're modding an SKX007, SRPD, or SNK
• You want the largest selection of aftermarket dials
• You prefer compact, refined watch builds

Choose 30.8mm if:

• You're building with the Seikonaut 40mm or Royal Oak 41mm
• You're modding a Turtle, Sumo, or Samurai
• You want a larger dial face for maximum readability
• You want Nautilus-specific dial designs

Still not sure? Start with your case. Every case on our store clearly lists the compatible dial size. Pick your case first, and the dial size follows automatically.

Frequently Asked Questions

What is the difference between 28.5mm and 30.8mm Seiko dials?

The numbers refer to the outer diameter of the dial disc. 28.5mm dials fit smaller cases (37-39mm) while 30.8mm dials fit larger cases (40-44mm). Both use the same NH35/4R movement, but the dial must match the case size.

Can I use a 28.5mm dial in a 40mm Seikonaut case?

Not directly. The 28.5mm dial would leave a visible gap in the 30.8mm opening. You'd need a spacer ring, which typically results in a subpar finish. We recommend using the correct 30.8mm dial size instead.

Which dial size has more aftermarket options?

28.5mm has significantly more options — it's the most common Seiko mod dial size because of the SKX007's popularity. However, 30.8mm selection is growing as larger mod cases become more popular.

Do both dial sizes use the same movement?

Yes. Both 28.5mm and 30.8mm dials fit the same NH35, NH36, NH38, NH70, NH71, NH72, and 4R-series movements. The movement doesn't change — only the dial and case differ.

How do I measure my current Seiko dial?

Remove the dial from the movement and measure the outer diameter with calipers. Measure across the widest point, not including the dial feet. You should get approximately 28.5mm or 30.8mm.

What happens if I install the wrong dial size?

A too-large dial (30.8mm in a 28.5mm case) simply won't fit. A too-small dial (28.5mm in a 30.8mm case) will sit loosely with a visible gap, and the chapter ring alignment will be off. Always match the correct size.

Are Nomods dials compatible with third-party cases?

Yes. Our 28.5mm dials work with any case designed for standard 28.5mm Seiko dials, and our 30.8mm dials work with any standard 30.8mm case. The feet positioning follows standard Seiko specifications.

Which dial size should I start with as a beginner?

28.5mm is the easiest starting point — more tutorials, more compatible cases, and more aftermarket choices. The Royal Oak 37mm case paired with a Waffle Dial is a great first build.

Read More

• Seiko Mod Dials: Complete Guide to Sizes, Styles & Selection
• 37mm Royal Oak Case: Full Specs & Build Guide
• Sapphire vs Hardlex Crystals
• Build Your Own Custom Seiko Watch
• Seiko Royal Oak Mods: Build & Buy Guide
• Are Seiko Nautilus Mods Worth It?
• NH72 Skeleton Movement Guide
• Shop All Seiko Mod Dials
• Browse All Seiko Mod Parts

Nomods is not affiliated with Seiko. All watches are independently built using Seiko-compatible NH movements and aftermarket components.