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Seiko watch · Prospex · automatic

Seiko SPB243

The Seiko SPB243 measures 38 mm across, 46 mm lug to lug, and 13 mm thick. It fits wrists from ~16.5 cm (flat-fit estimate).

Sources checked · How we source numbers
Case
38 mm1
Lug to lug
46 mm1
Thickness
13 mm1
Lug width
not published by Seiko
Seiko SPB243: size drawingSeiko SPB243, round case, top and side view to scale: case diameter 38 mm, lug to lug 46 mm, lug width — (unknown), thickness 13 mm. Bezel, dial and crown size are schematic.lug width —Ø 38lug to lug 46TOPthickness 13SIDE
Seiko SPB243, top and side, to scaleDrawing from data, not a photo · mm

Seiko SPB243 specifications

Case diameter
38 mm1seller listing
Lug to lug
46 mm1seller listing
Thickness
13 mm1seller listing
Lug width
not published by Seiko
Crystal
Sapphire1seller listing
Water resistance
200 m1seller listing
Movement
Seiko 6R351seller listing · automaticSeiko 6R35 specs
Battery
none: the Seiko 6R35 is automatic
Years made
start not published
Case code
not in our data yet

On your wrist

The verdict compares the lug to lug with the flat top of your wrist. Balanced from ~16.5 cm, past the edges below ~14.5 cm.

= 6.7 in

Balanced on a 17 cm wrist: the 46 mm lug to lug covers 84% of an estimated 54.8 mm flat top.

Flat top = circumference ÷ 3.1, a community convention, not a measurement of your arm. Compact ≤ 0.75 of the flat top, balanced ≤ 0.89, at the edge ≤ 1. Compare more watches in the watch size calculator.

Seiko SPB243: wrist fitSeiko SPB243 on a wrist, top view to scale. lug to lug 46 mm. Wrist 170 mm, estimated flat width 54.8 mm (circumference / 3.1). Ratio 0.84: balanced.wrist, flat topwrist flat ≈ 54.8lug to lug 46Balanced · 46 / 54.8 = 0.84estimate: wrist 170 / 3.1 = 54.8 flatcompactbalancededgeoverhang0.750.891
Seiko SPB243 on a 17 cm wristDrawing from data, not a photo · mm

Actual size on your screen

Calibrate once with a bank card and the drawing shows the Seiko SPB243 at 1:1, next to a millimetre ruler.

1:1 · not calibrated: sizes are approximate
Seiko SPB243: size drawingSeiko SPB243, round case, top and side view to scale: case diameter 38 mm, lug to lug 46 mm, lug width — (unknown), thickness 13 mm. Bezel, dial and crown size are schematic.lug width —Ø 38lug to lug 46TOPthickness 13SIDE
Drawing from data, not a photo · mm
01020304050

Seiko SPB243 strap size

Seiko publishes no lug width for the Seiko SPB243. Measure between the lugs with a caliper before buying a third-party strap.

Attachment: not published in our sources.

Find your strap length in the watch strap size tool, with the Seiko SPB243 filled in.

On a bracelet? How to remove watch links to size it to your wrist.

Movement: Seiko 6R35

The Seiko SPB243 runs on the Seiko 6R35, an automatic movement. 17 other models in our base use it.

Beat rate
21,600 bph2
Power reserve
70 h2
Jewels
242
Accuracy
−15 to +25 s/day2
Hacking seconds
Yes2
Hand winding
Yes2

Battery

none: the Seiko 6R35 is automatic

A mechanical watch has no cell to replace; it needs a service instead.

Same size as the Seiko SPB243

The models nearest to the Seiko SPB243 in case width and lug to lug, drawn over it to scale; below, every model within 1 mm of its 46 mm.

Size comparison: Seiko SPB243, Seiko SPB241, Seiko SPB245, Seiko SPB249Top-view outlines to scale on one centre. A Seiko SPB243: Ø 38, L2L 46, lug —, T 13. B Seiko SPB241: Ø 38, L2L 46.2, lug 19, T 12.9 (vs A: Ø 0 L2L +0.2 T −0.1). C Seiko SPB245: Ø 38, L2L 46.2, lug 19, T 12.9 (vs A: Ø 0 L2L +0.2 T −0.1). D Seiko SPB249: Ø 38, L2L 46.2, lug 19, T 12.9 (vs A: Ø 0 L2L +0.2 T −0.1).A Ø 38B Ø 38C Ø 38D Ø 38A L2L 46B L2L 46.2C L2L 46.2D L2L 46.2A Seiko SPB243Ø 38 · L2L 46 · lug — · T 13B Seiko SPB241Ø 38 · L2L 46.2 · lug 19 · T 12.9vs A: Ø 0 L2L +0.2 T −0.1C Seiko SPB245Ø 38 · L2L 46.2 · lug 19 · T 12.9vs A: Ø 0 L2L +0.2 T −0.1D Seiko SPB249Ø 38 · L2L 46.2 · lug 19 · T 12.9vs A: Ø 0 L2L +0.2 T −0.1
A Seiko SPB243 and the 3 nearest in size, on one centre, to scaleDrawing from data, not a photo · mm

Nearest in size

  1. ASeiko SPB243this watch
  2. BSeiko SPB241W same · L2L +0.2 · T −0.1 mm
  3. CSeiko SPB245W same · L2L +0.2 · T −0.1 mm
  4. DSeiko SPB249W same · L2L +0.2 · T −0.1 mm

Differences against A in mm: W case width, L2L lug to lug, T thickness. Nearest by width and length together, from the published sizes.

Same movement: Seiko 6R35

All 18 models on the Seiko 6R35

Seiko SPB243 questions

How big is the Seiko SPB243?

The Seiko SPB243 measures 38 mm across, 46 mm lug to lug, 13 mm thick.

Will the Seiko SPB243 fit a 6.5-inch wrist?

Balanced: the Seiko SPB243's 46 mm lug to lug takes 86% of the ~53.3 mm flat top of a 6.5-inch (16.5 cm) wrist. By the same estimate (circumference ÷ 3.1) it sits balanced from about 16.5 cm and overhangs the flat top on wrists under about 14.5 cm.

Does the Seiko SPB243 need a battery?

No. The Seiko SPB243 has no cell to replace: a wound mainspring drives its automatic Seiko 6R35.

What movement is in the Seiko SPB243?

The Seiko SPB243 runs on the Seiko 6R35, an automatic movement.

More Seiko watches

Sources

Documents checked · Report a wrong number

  1. 1Right Time International — SPB243 listing, Right Time (Denver), dealer spec block (listing, sold out) · html · read
  2. 2Seiko Watch Corporation — Diver's watch for air diving instructions, Cal. 6R35 (EN) · pdf · read
  3. 3CaliberCorner — Seiko Caliber 6R35 watch movement page · html · read
  4. 4Grail Watch — Grail Watch Reference: Seiko 6R35 · html · read