Subaru Legacy Back Up Light Bulb Size

The Subaru Legacy back up light utilizes 1157, 921, 1156, and P21W bulb sizes depending on the specific version of the vehicle. Available information covers a range of years starting from 1990 through 2024.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2023-2024	1157
2008-2022	921
1990-1999	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The Subaru Legacy backup light specifications reference three distinct bulb types across the model's history: the 921, the 1156, and the 1157, each carrying a different base design and filament configuration.
The 921 is a T15 wedge-base bulb rated at 12V and 16W. Its wedge construction means it is held in place by socket tension rather than a bayonet locking mechanism.
The 1156 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W. The BA15s base features a single contact pin, which physically prevents substitution with dual-pin bayonet bulbs.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 21W and 5W respectively. Its offset pins distinguish it from the single-pin BA15s base used by the 1156.
All three bulb types conform to ANSI standards recognized in the United States and Canada, indicating standardized electrical and physical tolerances across manufacturers.
The Subaru Legacy (2008-2022) specifies the 921 wedge bulb for the backup light position, representing the longest continuous fitment period across the specifications provided.
The 2023-2024 Legacy models specify the 1157 dual-filament bulb, which differs in both base type and filament count from the 921 used in prior model years. These bulbs are not interchangeable.
The 1990-1999 Legacy models specify the 1156 single-filament bayonet bulb. Despite sharing a 21W rating with the 1157, the differing base configurations make the two bulbs physically incompatible with each other's sockets.
The 921 wedge base and the 1156 or 1157 bayonet bases represent fundamentally different socket systems, meaning no cross-substitution is possible between wedge-type and bayonet-type bulbs without a socket adapter.
The 1157 and 1156 share the same 15mm bayonet base collar width, but the 1157 has two offset pins while the 1156 has one, a distinction that prevents accidental installation of one in place of the other.