Seiko Caliber 8L45 Watch Movement

Manufacturer	Seiko
Caliber Number	8L45, 8L45A
Base Caliber	Grand Seiko 9S65
Evolution Of	Seiko 8L35
In-House?	Yes
Movement Type	Automatic, self-winding mechanical
Diameter	28.4mm
Height	6mm
Jewel Count	35 jewels
Beat Rate / Frequency	28,800 bph / 4 Hz
Accuracy Rating	-5/+10 seconds/day
Lift Angle	53 degrees (unconfirmed)
Power Reserve	72 hours
Rotor Direction	Bidirectional (Magic Lever)
Hand-Windable?	Yes
Anti-Shock Device	Diashock
Mainspring/Hairspring	Seiko SPRON
Hand Count	3
Functions	Central hours; central minutes; central sweeping seconds; date at 3:00
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	Seiko Prospex Marinemaster Professional 60th Anniversary Limited Edition (Ref: SLA081), King Seiko VANAC (Ref: SLA083, SLA085, SLA087, SLA089, SLA091) (Add your watch to the comments below…)

The Seiko caliber 8L45 is a 3-hander automatic watch movement with a date. This movement is found in various King Seiko models, as well as the Seiko Prospex Marinemaster Professional 60th Anniversary Limited Edition dive watch that was introduced in March 2025.

In Seiko’s own words:

“Caliber 8L45 achieves a power reserve of 72 hours thanks to an improved mainspring, and it has an accuracy of +10 to –5 seconds per day. It was engineered to have the robustness and other qualities demanded of movements that power modern-day mechanical sports watches. The movement features exquisite wave patterns on the rotor and bridges, adding a touch of luxury and refinement to its design. Through its combination of high performance and functional beauty, Caliber 8L45 represents the pinnacle of Seiko’s mechanical watch movements.” –Source

At the time of its release, Seiko claims that the 8L45 is their “most precise mechanical movement in production”:

“The watches are equipped with the new Caliber 8L45, Seiko’s most precise mechanical movement in production, achieving a stable accuracy range of +10 to -5 seconds per day. ” –Source

Some of the topics covered in this caliber listing:

8L45 VS 8L35:

	8L45	8L35
Jewels	35	26
Power Reserve	72 hours	50 hours
Accuracy Rating	-5/+10 seconds/day	-10/+15 seconds/day

Most of the specs are the same between the 8L45 and previous 8L45 – except for jewel count, power reserve, and accuracy rating.

It is still unclear as to the locations of the additional 9 jewels, but Seiko attributes the increased performance (accuracy and power reserve) to the 8L45’s redesigned mainspring:

“With Caliber 8L45, Seiko has improved the shape and design of the mainspring and implemented precise accuracy adjustments, achieving the most stable accuracy (-5 to +10 seconds per day) among Seiko’s current mechanical movements and a power reserve of approximately 72 hours.” –Source

Seiko 8L45 VS Grand Seiko 9S65:

It is interesting to note that the GS calibre 9S65 that the 8L45 is said to be based on, is also equipped with 35 jewels and offers 72 hours of runtime. The 9S65 was introduced in 2010 with these specs – and tuned to an average accuracy of -3/+5 seconds/day.

Therefore, it should not be lost on the community that what Seiko calls their most precise movement to date was actually available from their Grand Seiko division 15 years before the 8L45 was announced – and with a far better accuracy rating.

Power Reserve:

The caliber 8L45 holds a power reserve of at least 72 hours. To fully wind the mainspring, turn the crown a minimum of 55 times.

As mentioned above, this mainspring is new for the 8L series, but Seiko elaborates more about it below…

“The new Caliber 8L45 represents the pinnacle of Seiko’s mechanical watch movements. It incorporates Spron, Seiko’s proprietary alloy, designed for durability against breakage, rust, and wear, ensuring resilience in harsh underwater conditions. A thinner, longer mainspring provides 72 hours of power reserve, while an improved method for securing the movement within the case enhances durability. In addition to its longer power reserve, Caliber 8L45 operates within a tolerance of +10 to -5 seconds per day.” -Official press-release, March 6, 2025 (source)

Crown Position Functions:

0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
1 (pulled out one click): Clockwise = Date setting / Counterclockwise = Nothing
2 (pulled out two clicks): Time setting clockwise and counterclockwise

Can you overwind the 8L45?

No. According to the Seiko documentation, manually winding the movement after it is already fully wound will not break the spring.

When can you adjust the date?

To avoid damaging your watch movement, do not adjust the date between 8:00 PM and 2:00 AM.

How often does the 8L35 need serviced?

According to official Seiko documentation, watches with the caliber 8L45 should be overhauled every 2-3 years. Learn all about Seiko service intervals here. At the time of this post, the starting cost of getting this movement services by Seiko is $398.00 USD.