T8 bulb shape and size

Dimensions

What T8 tells you

Shape

one-inch tubular lamp

Nominal diameter

1 in (25 mm)

Typical bases

G13

Common uses

troffers, shop lights, utility 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 T8

• A G13 base does not prove ballast compatibility.
• LED tubes may be ballast-compatible, ballast-bypass, or hybrid.

Sources

Reference method

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

• LEDVANCE guide to light bulb shapes, types, and sizes
• U.S. Department of Energy: lumens and lighting choices