The median is 48 seats
Across the 486 shops with a seat count, the median is 48 — ordinary for Japan. Picture a normal room with a mix of tables and counter.
The spread is wide, though. Eleven shops seat 10 or fewer, 16 seat 12 or fewer, 61 seat 20 or fewer. At the other end, 108 seat 80 or more. Those two extremes make for completely different experiences when you arrive by yourself.
Small rooms are the easy ones
The 16 shops at 12 seats or under are almost all counter-only. They were built assuming solo customers, and the layout makes it irrelevant who sits beside you.
A Japanese counter is designed as a place to come alone. Nobody will make conversation, and eating in silence and leaving is entirely normal. These are the shops foreign visitors find most intimidating, and they are in fact the most suited to eating alone.
Big rooms are where you stand out
The 108 shops seating 80 or more are mostly izakaya and yakiniku. Their customers are groups and families, and the seating is built for that.
You will not be turned away as a rule. But you may be walked to a table for four, which serves neither you nor the shop, and at peak times a refusal is possible. Seat counts are printed on every shop page — if you are alone, read the number before you commit.
Choosing by dish instead
Noodles and set meals suit solo diners best: ramen, miso-nikomi udon, kishimen, ankake spaghetti, teishoku. Each is a complete single portion and finishes at the counter.
The hard ones are yakiniku and multi-course washoku — the unit of ordering is large and assumes several people. Yakitori and kushikatsu sit in between, since you order one skewer at a time.
Lunch makes all of it easier
The same restaurant runs a higher share of solo customers at midday, because people working nearby come in to eat. Even a large room feels normal alone at lunch.
The price drops too. If a place felt hard to enter alone in the evening, go back the next day at noon. It is the same kitchen.
Practical notes
Hold up one finger at the door and "table for one" is communicated. Nothing more is needed.
If you are shown to a counter, bags go in the basket at your feet. Walking into a small shop with a full-size suitcase is genuinely difficult, so leave it in a station locker or a luggage room before you set out.