Seiko Caliber 6r20

Seiko Caliber 6R20

Seiko Caliber 6r20

Manufacturer Seiko
Caliber Number 6R20, 6R20A
Movement Type Automatic, self-winding mechanical
Diameter 27.40mm (outside), 27mm (casing)
Height 6.15mm
Total Parts
Jewel Count
Vibrations Per Hour
28,800 bph (4Hz, 8 beats per second)
Lift Angle
52 degrees
Shock System? Diashock
Mainspring Spron 510
Power Reserve
~45 hours
Rotor Winding Direction
Bi-directional (Magic Lever)
Hacking Seconds? Yes
Hand-Windable? Yes
Magnetic Resistance
4,800 A/m (60 gauss)
Hands Count
Functions Central hours, central minutes, central sweeping seconds, power reserve indicator between 8:00 and 11:00, day of the week subdial at 3:00, date subdial at 6:00
Country of Manufacture Japan
Known Models
Seiko Premier SPB001 (Add your watch in the comments below)

The Seiko caliber 6R20 is an in-house automatic movement with a power reserve indicator and day-date subdials style calendar complication. The movement is part of Seiko’s 6R family of movements and is made in Japan.

Seiko 6420a


The general caliber number is 6R20, with 6R20A being the first version. The subsequent letter variations indicate evolution stages in the movements development. Early models of the 6R20 At the time of this post, the latest and current version of this movement is the 6R20A (if this changes, please update the comments below).

Base Caliber:

The caliber 6R15 is the base caliber for 6R series movements such as the 6R20 discussed here (as well as the 6R21, and 6R24, and 6R27). Interesting note: The calibre 6R20 shares the same instruction manual as the 6R21, 6R24 and 6R27 movements.

6R20 VS 6R15:

Although based on the 6R15 framework, the 6R20 reads much differently on paper – and on the wrist. A few of the differences are outlined in the chart below:

6R15 6R20
Height 5.25mm 6.15mm
Total Components 168 208
Jewels 23 29
Beat Rate
21,600 (6 beats/second) 28,800 (8 beats/second)
Lift Angle
53 52
Features Central hours, central minutes, central seconds, date at 3:00 Central hours, central minutes, central sweeping seconds, power reserve indicator between 8:00 and 11:00, day of the week subdial at 3:00, date subdial at 6:00

6R20 VS 6R21:

There is a similar caliber 6R21 with the main difference being the power reserve indicator display style. On the 6R20, the PR indicator spans from 8:00 (empty) to 11:00 (full), with the indicator hand being closer to the edge of the dial. On the 6R21, the PR indicator spans from around 7:00 (full) to 11:00 (empty), with the pointer hand positioned closer to the center of the dial.

In Seiko’s own words, they describe the placement on the 6R20 as being “center aspect” and the 6R21 as “9 o’clock aspect”. Also note: the span locations may vary depending on model.

Seiko 6r20 Vs 6r21


Seiko claims that the cal. 6R20 has an average accuracy rating of -15/+25 seconds per day in normal temperature conditions (between 5 – 35 degrees C).

Seiko says this about accuracy:

  • The accuracy of mechanical watches may not fall within the specified range of time accuracy because of loss/gain changes due to the conditions of use, such as the length of time during which the watch is worn on the wrist, arm movement, whether the mainspring is wound up fully or not, etc.
  • The key components in mechanical watches are made of metals which expand or contract depending on temperatures due to metal properties. This exerts an effect on the accuracy of the watches. Mechanical watches tend to lose time at high temperatures while they tend to gain time at low temperatures.
  • In order to improve accuracy, it is important to regularly supply energy to the balance that controls the speed of the gears. The driving force of the mainspring that powers mechanical watches varies between when it is fully wound and immediately before it is unwound. As the mainspring unwinds, the force weakens.
  • Relatively steady accuracy can be obtained by wearing the watch on the wrist frequently for the self-winding type and winding up the mainspring fully everyday at a fixed time to move it regularly for the wind-up mechanical type.
  • When affected by external strong magnetism, a mechanical watch may loss/gain time temporarily. The parts of the watch may become magnetized depending on the extent of the effect. In such a case, consult the retailer from whom the watch was purchased since the watch requires repair, including demagnetizing.

Power Reserve:

The caliber 6R20 holds a power reserve of at least 45 hours. To fully wind the mainspring, turn the crown a minimum of 55 times.

Crown Position Functions:

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

Stem Removal:

To remove the stem, make sure the crown is in position 0 or normal position (not date or time setting position). There is a lever with a small indentation for your tool. Gently press down while pulling the stem out. See official instructions below for more guidance:

Seiko Caliber 4r36 Stem Removal


Macro Images:

Below is a close-up view of the 6R20 Dia-shock anti-shock protection device, as well as the Etachron regulator, balance wheel and balance spring.

Seiko 6r20 Diashock

Examples of watches with this caliber:

The 6R20 shown here was found in this Seiko Premier SPB001 watch with dial reference 6R20-00A2, and case reference 6R20-00A0. The caseback is also marked with “KG” and “A4” in a box.

Seiko Premier Spb001 Caliber 6r20 00a0 Automatic Movement

Caliber Commentary:

Watchhound posted a review of the SPB001 (pictured above) here:

I have worn this watch for about a month now, and it is as good as the watch forums say, in quality and appearance. And, there was a slight “break-in” period where the watch ran a little fast during the day or when resting face-up, and slower when on its side. But now, it stays within a second or two a day, sometimes better! It seems to perform like a quartz watch. It is truly amazing, you will want to wear this watch all the time, to keep it running. Also at night, you can hear it tick with a slight ring or ting, it sounds very well-made, and the fast beats (8 per second) are sort of “intense” sounding. Great watch, I had bought an ESQ automatic which looked great, but ran horribly (even after getting the movement replaced under warranty). Seiko has it down pat.

Additional Resources:

Seagull Caliber St19

Join our mission to spread movement awareness!

Members Online

  • admin Spokesfield eugenio

Recent Forum Posts

Trending Comments

Hans Groenewegen

Orient Caliber F6922

I've had my Mako and Ray Orient watches with these calibers, I guess. Their performance…


Miyota Caliber 2115

Found in a Kenneth Cole “Unlisted” brand watch.


Miyota Caliber 2035

The super 2035 is gold plated.


Sellita Movement Grades

Yes. The diameter and height will be the same. The main differences are the finishing,…


Sellita Movement Grades

Can they be exchanged ie upgraded? Same dimensions?


Would love your thoughts, please comment.x