What is the standard formula for sizing a lampshade to a table lamp base?
The shade diameter should be roughly twice the base diameter, and the shade height should be two-thirds the height of the base itself.
The two-thirds rule is the professional starting point for every shade-to-base pairing. Measure your base from its foot to the bottom of the bulb fitting — exclude the fitting itself. Multiply that figure by 0.66 to get the target shade height. For width, measure the widest point of the base and double it to get the shade's bottom diameter.
So a base that is 30cm tall and 12cm wide at its broadest point calls for a shade roughly 20cm tall and 24cm wide at the bottom. These are proportional targets, not rigid specifications — a shade 2–3cm either side of those figures will still read as balanced.
The rule applies across the most common base profiles found in table lamps: column, urn, and cylindrical forms. Bases with unusual silhouettes — very narrow columns or wide squat forms — need individual adjustment, which the sections below address.
Always check the shade's top diameter too. A shade with a very wide top opening can expose the bulb and fitting at certain viewing angles, which looks unfinished. The top opening should sit below the lower edge of the bulb holder by at least 2–3cm.
How do lampshade fittings affect which shade you can use?
Lampshade fitting type — duplex, pendant, or gimbal — determines whether a shade physically attaches to your base, regardless of size.
Three fitting types cover the vast majority of UK table lamp shades.
- Duplex fitting: a ring that sits on a shade carrier attached to the lamp's bulb holder. Standard on most UK table lamps. The carrier screws onto an ES (E27) or BC (B22) holder.
- Pendant fitting: a single central hole at the top of the shade, used on pendant-style lamps. Not compatible with a standard table lamp base without an adapter.
- Gimbal fitting: two arms that grip the shade from the sides, used on some adjustable or architectural bases.
Before ordering a shade, confirm your base uses a shade carrier (duplex). If it does, any duplex shade in the correct size range will fit. The carrier ring diameter is almost always 30mm on UK bases, so this is rarely a variable.
One practical check: with the shade carrier in place and the shade seated on it, the bottom edge of the shade should clear the table surface by at least 5cm. A shade that sits too low obscures the base entirely and creates uncomfortable glare at seated eye level. The Energy Saving Trust notes that top energy saving ideas for home improvement include choosing the right shade depth to maximise light output from efficient bulbs rather than trapping it inside a deep drum.
How do you size a shade for a very tall or very short base?
Tall bases above 45cm need shades at least 30cm wide to avoid a top-heavy look; short bases under 20cm suit tight drum shades of 15–20cm diameter.
The two-thirds rule holds mathematically at any scale, but visual balance can break down at the extremes. A 50cm column base calculated to need a 33cm-tall shade will look correct only if the shade is also wide enough — at least 30cm at the bottom, ideally 35cm. A narrow shade on a tall base reads as pinched.
For short bases — bedside lamps, accent lamps, cube bases like the Aeriz Wood Cube at 10cm wide — the shade needs to be proportionally compact. A drum shade of 15–18cm diameter and 12–15cm height keeps the assembly neat without the shade overwhelming the base. Avoid empire-profile shades on very short bases; the flared bottom extends too far and the lamp looks unstable.
With mid-height bases in the 25–35cm range, the formula works without adjustment. This is the most common table lamp size in UK residential use, and the widest range of off-the-shelf shades is designed for exactly this proportion.
For a two-light base such as the Puntes Gold at 58cm, treat each fitting arm independently for shade sizing, then confirm both shades clear each other by at least 3cm when seated. Paired shades on a single base must match exactly — diameter, height, and profile.
Does shade shape affect the light output from a table lamp?
Shade shape directly controls light distribution — drum shades spread light evenly up and down, while empire shades direct more light downward onto surfaces.
Drum shades have parallel sides and distribute light in a roughly equal split: upward through the top opening and downward through the bottom. This makes them effective for ambient lighting in living rooms and bedrooms, where you want the ceiling to receive some reflected light.
Empire shades taper from a narrow top to a wide bottom. The angled sides direct a larger proportion of light downward, making them better for task positions — a reading chair, a writing desk, a bedside table where you need directed illumination rather than general fill.
Coolie shades (very wide, very shallow) produce a broad downward wash with minimal upward light. They suit low-level accent positions where you want a wide pool of light on a surface.
Shade material matters as much as shape. Opaque fabric or metal shades produce hard cut-off lines and concentrate output. Translucent linen or cotton diffuse the light and create a softer glow through the shade itself — useful for evening ambience but less efficient for task use. The Energy Saving Trust's guidance on saving energy in the kitchen highlights that directing light where it is needed rather than diffusing it generally reduces the wattage required to achieve the same useful illumination. The same principle applies to table lamp placement throughout the home.