Lamp Shade Size Calculator

Calculator

Units

Lamp type

Shade shape

Environment

Light goal

Fitter type

Base height

Measure from base bottom to socket base.

Base width / diameter

Use the widest point of the base.

Optional harp height

If known, improves accuracy.

Bulb type

Bulb wattage / equivalent

Used to suggest safer clearance.

Example Data Table

Scenario	Base height	Base width	Shape	Suggested top	Suggested bottom	Suggested height
Path lamp, outdoor, ambient	42 cm	16 cm	Drum	24.5 cm	30.5 cm	28.6 cm
Patio table lamp, indoor, task	50 cm	20 cm	Empire	23.5 cm	39.0 cm	30.7 cm
Floor lamp, indoor, ambient	120 cm	28 cm	Bell	30.5 cm	55.0 cm	61.8 cm

Examples are illustrative. Always confirm fitter hardware and clearance.

Formula Used

Shade height: shadeHeight = baseHeight × factor, where factor depends on lamp type (table ≈ 0.67, floor ≈ 0.50, post ≈ 0.55).
Bottom size: blended target using baseWidth and baseHeight, then bounded to 1.4×–2.6× baseWidth.
Top size: top = bottom × ratio, where ratio depends on shape (drum ≈ 0.80, empire ≈ 0.60, bell ≈ 0.55).
Slant height: slant = √(((bottom − top)/2)² + height²) for tapered shades.
Clearance: clearance based on bulb type, with extra margin for higher wattage.

How to Use This Calculator

Measure lamp base height from the bottom to the socket base.
Measure the widest base width or diameter, including curves.
Select your lamp type and shade shape that matches your style.
Choose bulb type and wattage to get a safer clearance suggestion.
Press Calculate, then download results as CSV or PDF.

Proportion Rules That Keep Fixtures Balanced

This calculator sizes a shade by relating it to the lamp base, then refining the result for shape and use. A practical starting point is shade height at about 50–67% of base height. Shorter ratios suit tall floor fixtures, while path and table lamps often look best near two‑thirds because the socket is covered without hiding the body. If your base is strongly curved, measure the widest point for width and the full vertical height; those two numbers drive the most reliable outputs.

Bottom Size Based on Base Width

The bottom opening controls the visual footprint and how much light escapes downward. The model blends base width and base height, then constrains the bottom size to a typical range of 1.4× to 2.6× the base width. Staying inside this band helps prevent wobble in outdoor breezes and avoids the “mushroom cap” look on small garden posts.

Top Size and Shade Shape Taper

Top size is calculated as a ratio of the bottom size. Drum shades remain closer to the bottom for a modern, even glow. Empire and bell shapes taper more, opening the lower area for pathway illumination and reducing harsh bulb visibility. For tapered shades, slant height is computed to estimate the panel length you may need when building or ordering.

Heat Clearance for Safer Materials

Clearance is estimated from bulb type and power. Cooler sources allow tighter spacing, while hotter bulbs require more air gap to protect fabric, coatings, and wiring. The calculator outputs a recommended clearance and a harp height estimate, making it easier to keep the shade centered while maintaining safer separation during longer evening run times.

Outdoor Practical Checks Before Purchase

For gardens and patios, confirm UV‑stable materials, corrosion‑resistant hardware, and drainage or venting so moisture does not collect. Also verify fitter type and diameter, because spider, uno, and clip‑on fitters sit at different depths. Use the download buttons to save the exact numbers for your supplier or installer.

FAQs

1) Which measurement matters most for shade sizing?

Base width (or diameter) drives the bottom size, which controls overall visual balance. Base height then guides shade height so the fixture does not look stretched or cramped.

2) Should outdoor shades be larger than indoor shades?

Often slightly, because outdoor sightlines and glare control are different. A modest increase in height can reduce direct bulb visibility while keeping proportions aligned with the base.

3) How do I pick between drum, empire, and bell?

Drum provides a modern, even spread. Empire gives a classic tapered look and broader bottom opening. Bell softens the silhouette and can direct more light downward for pathways.

4) What clearance is considered safe?

It depends on bulb heat. LEDs need less clearance than hotter bulbs. Always follow bulb and shade material ratings, and keep fabric from touching the bulb or socket parts.

5) Why does the fitter type affect results?

Different fitters change how the shade sits relative to the socket and harp. That changes the effective drop and can alter how much bulb is hidden and how evenly light spreads.

6) Can I trust the result if my base is curved?

Yes, if you measure the widest point of the base for width and the full vertical height for height. For unusual shapes, consider testing a size one step up or down.