Edison Screw Size Table
| Designation | Major diameter | Pitch (mm) | Trade name | Typical application |
|---|---|---|---|---|
| E5 (E5.5) | 5.5 mm | 1 | Lilliput Edison Screw (LES) | Indicator and decorative lights |
| E10 | 10 mm | 1.81 | Miniature (MES) | Flashlights, bicycle lights |
| E11 | 11 mm | — | Mini-Candelabra | 120 V halogen mini-candelabra |
| E12 | 12 mm | 2.6 | Candelabra (CES) | 120 V candelabra, night lamps |
| E14 | 14 mm | 2.82 | Small (SES) | 230 V chandeliers, night lamps |
| E17 | 17 mm | — | Intermediate (IES) | 120 V appliances, decorative |
| E26 | 26 mm | — | Medium (ES) | Standard 120 V lamps |
| E27 | 27 mm | 3.62 | Edison Screw (ES) | Standard 230 V lamps |
| E39 | 39 mm | — | Mogul | 120 V 250+ W industrial |
| E40 | 40 mm | 6.35 | Goliath (GES) | 230 V 250+ W industrial |
Every screw-in lamp in the world descends from one 1880s thread, and the whole family is named by a single number: the E-code is the major thread diameter in millimeters, rounded. E14 is about 14 millimeters across the threads, E27 about 27 - that is the entire naming rule, and once you know it the chart below reads itself. The trade names map onto the numbers: the candelabra E12 in North America, the small E14 in Europe, the medium E26/E27 household pair, the mogul E39 and the Goliath E40 for the big industrial lamps. The IEC 60061 standard sheet numbers in the last column are the official identity when a datasheet needs one.
The one-millimeter trap sits in the middle of the table: E26 and E27 are physically near-twins serving different power grids. E26 is the 120-volt North American standard, E27 the 230-volt European and world standard; the extra millimeter of thread diameter keeps the two ecosystems nominally distinct. A 26 bulb will start in a 27 socket and often light, but the contact geometry is wrong - the pin contact can sit poorly, run hot, or fail inspection on commercial fixtures, so the honest rule is: same number region, same voltage system, same bulb. The screw is a mechanical interface, not a voltage converter - pairing the right base with the right supply is the same discipline as pairing the right plug to the right outlet.
How to use
- Measure or read before buying: the E-code is printed on the bulb base or fixture socket; if it is worn off, measure the thread outer diameter in millimeters and match the nearest E number in the chart diameter column.
- Check the name column for the trade synonym: listings say CES for E12, SES for E14, ES or medium for E26/E27, Goliath for E40 - the letters vary by region and vendor but the E number is the universal cross-reference.
- Mind the voltage system with the near-twin sizes: E26 belongs to 120 V fixtures and E27 to 230 V - if you are moving lamps between regions, verify the whole lamp, not just the base, and see the plug-type reference for the outlet side.
Frequently asked questions
Will an E26 bulb work in an E27 socket, or the other way round?
Mechanically it often threads in; electrically it is out of spec. The threads overlap enough that a 26 mm bulb engages a 27 mm socket, and in a pinch it may light - but the difference is not just diameter: E26 and E27 carry slightly different thread profiles, and the center-contact height differs, so the pin contact can rest on the solder blob instead of seating cleanly. The practical symptoms are flicker, heat at the base, and intermittent contact; the worst case is a commercial or rental fixture failing inspection, because no standard covers the cross-pair. Buy the number your fixture specifies: E26 for North American 120 V fittings, E27 for 230 V. The one-millimeter question has a one-line answer - near fits are for emergencies, correct fits are for purchases.
What is the difference between candelabra, intermediate and standard bases?
They are the everyday steps of the size ladder in North America: candelabra E12 (12 mm, called CES) is the small candle-bulb base on chandeliers, sconces and night lamps; intermediate E17 (17 mm, IES) sits between it and standard, common in appliance bulbs, older ceiling fans and decorative fixtures; standard or medium E26 (26 mm, ES) is the default household base. Europe collapses the same roles onto E14 (small, SES) and E27 (standard), skipping the intermediate size almost entirely. The trap when buying shades or fixture conversions is the name column: candelabra and chandelier both describe E12, small and SES both describe E14, and a shade sold for a chandelier clip may fit either. Match the E number, then confirm with the diameter column - the names are marketing, the millimeters are physics.
Why does the E number measure the thread diameter, and what about the pitch column?
The E-code system dates from the first Edison lamps and encodes exactly one dimension - the outside diameter of the thread - because that single number fixed the whole brass shell and socket pairing at the machine-shop level. The thread pitch column in the chart adds the second mechanical fact: these are real screw threads with defined lead, E27 at 3.62 mm and E14 at 2.82 mm, coarser than most machine threads because the lamp must engage in half a turn and lock under finger pressure alone. That is why the numbers in the pitch column read like metric thread series values - they are, in all but formality - and why a lamp base will never cross onto a standard bolt thread even where diameters land close: different flank form, different tolerance class, and no locking taper. For threading questions generally, the metric pitch table shows the same vocabulary in its native habitat.
What are E39 and E40 mogul and Goliath bases used for today?
They are the big-end of the family, and they exist for heat and wattage, not novelty. The mogul E39 serves 120 V industrial lamps - high-bay warehouse fixtures, street lighting, agricultural grow lamps - where a fatter shell carries the higher current and spreads the heat that would cook a smaller base. The Goliath E40 is its 230 V counterpart in Europe and in high-wattage HID lamps worldwide. Everyday LED technology has shrunk actual wattage so far that new residential fixtures almost never need these sizes, but the installed industrial base keeps them alive: replacing a 400-watt high-bay lamp still means an E39 or E40 order, and the IEC 60061 sheets in the chart (7004-24 and 7004-24A) are the official references a facilities buyer will meet on datasheets. Practical tip for LED conversions: the retrofit lamps keep the same bases, so the fixture stays - just verify the driver clearance before ordering the bigger retrofit.