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General A shapes

A21 bulb shape and size

A21 is the large a-shape bulb designation. Its nominal maximum diameter is 2.625 inches. A21 may not clear a shade sized for A19. The base, voltage, light output, and exact overall length come from the individual lamp specification.

Representative family profile and nominal maximum diameter only. Overall length is not to scale, and the base is intentionally omitted.

Dimensions

What A21 tells you

Shape
large A-shape bulb
Nominal diameter
2.625 in (67 mm)
Typical bases
E26
Common uses
high-lumen lamps, garage fixtures, open ceiling fixtures

The diameter is part of the naming system, not a full dimension drawing. Individual models can differ in overall length, neck profile, optics, and manufacturing tolerance. Use the maker's drawing when the fit is close.

At the fixture

Four other details to record

  1. Read the base code and voltage on the old lamp or fixture label.
  2. Compare the published maximum diameter and overall length with the available space.
  3. Record lumens, beam angle where relevant, color temperature, and dimming behavior.
  4. Look for the enclosure, location, temperature, or vibration rating required by the fixture.

Easy to miss

Notes for A21

  • A21 may not clear a shade sized for A19.
  • Match lumens rather than equivalent-watt marketing alone.

Sources

Reference method

BulbMatch uses the U.S. eighth-inch naming convention as a nominal shape reference and keeps model-specific dimensions separate.