Bulb Shapes and Sizes

Bulb shape codes tell you two things: the letter(s) describe the shape, and the number is the diameter in eighths of an inch. So an A19 is an A-shape bulb 19/8" (2-3/8") across, and a BR30 is a bulged reflector 30/8" (3-3/4") across. The chart below shows every common shape at a glance.

Light bulb shapes and sizes reference chart: A, PS, B, C, CA, RP, S, F, R, MR, BR, G, T, BT, E, ED, AR, PAR series, linestra, linear and compact fluorescent

Shape Series Quick Reference

A Series (Arbitrary/Standard household): A15, A17, A19, A20, A21, A23 — the classic household bulb shape. A19 is the standard.

PS Series (Pear Straight): PS25, PS35 — oversized pear-shaped bulbs, often high wattage.

B Series (Blunt tip/Torpedo): B8, B10, B11, B13 — decorative torpedo-shaped candelabra bulbs.

C Series (Candle/Cone): C6, C7, C9, C11, C15 — the classic Christmas-light and night-light shapes.

CA Series (Candle Angular/Flame tip): CA5, CA7, CA8, CA10, CA11 — bent-tip decorative flame bulbs.

RP & S Series (Round Pear & Sign): RP11, S6, S8, S11, S14, ST18 — sign, marquee, and vintage Edison-style shapes.

F Series (Flame): F10, F15, F20 — textured flame-shaped decorative bulbs.

Prism: faceted decorative bulb.

R Series (Reflector): R12, R14, R16, R20, R25, R30, R40 — smooth-dome reflector floods for recessed and track fixtures.

MR Series (Multifaceted Reflector): MR8, MR11, MR16, MR20 — compact low-voltage spot/flood lamps, common in track and landscape lighting.

BR Series (Bulged Reflector): BR25, BR30, BR38, BR40 — wide-beam floods; BR30 is the standard for residential recessed cans.

G Series (Globe): G9, G11, G12, G16, G16½, G19, G25, G30, G40 — round globe bulbs for vanities and pendants.

T Series (Tubular): T3, T4, T4½, T5, T5½, T6, T6½, T7, T7½, T8, T9, T10, T14, T20 — tube-shaped bulbs for appliances, exit signs, and showcases.

BT Series (Bulged Tube): BT15, BT28, BT37, BT56 — HID lamp shapes for industrial fixtures.

E & ED Series (Ellipsoidal / Ellipsoidal Dimpled): E17, E18, E23½, E23, E37, E25, ED17, ED18, ED23, ED23½, ED28, ED37 — HID lamp envelopes.

AR Series (Aluminum Reflector): AR70, AR111 — precision low-voltage reflector lamps.

PAR Series (Parabolic Aluminized Reflector): PAR14, PAR16, PAR20, PAR30 Short Neck, PAR30 Long Neck, PAR36, PAR38, PAR46, PAR56, PAR64 — directional beam lamps for outdoor floods, theater, and display lighting.

Specialty: JC Bi-Pin, Wedge, Festoon, Rigid Loop — miniature halogen and automotive/landscape shapes.

Linestra: T10 double-ended linear incandescent.

Linear Fluorescents: T2, T4, T5, T8, T12 — tube diameter in eighths of an inch (a T8 is 1" across).

Compact Fluorescent Coils: T2 Coil, T3 Coil, T4 Coil — spiral CFLs.

Compact Fluorescent Plug-In Lamps: Twin Tube, Triple Tube, Quad Tube.

Not sure which shape you're holding? Check the etching near the base, or see our Bulb Bases and Filaments chart — between the two, you can identify almost any lamp. Still stuck? Send us a photo and we'll identify it for you.