The most common lighting mistake in an American home is not the wrong style. It is the wrong size: a fixture too small for the room, hung too high, so the table below it looks unfinished no matter what else you put in there.

There are three numbers that fix it, and they take about two minutes to work out. Then you pick whatever you like the look of.

Number one

How wide the fixture should be

Add your room's length and width in feet, then read that total as inches. A 12 x 15 ft dining room comes to 27, so you want a fixture around 27 in across.

If it hangs over a table, the table wins. The fixture should span roughly one half to two thirds of the table's width. A 42 in round table wants something 21 to 28 in across. Go wider than two thirds and people knock their heads reaching across.

Number two

How high to hang it

Over a dining table or a kitchen island, leave 30 to 36 in between the bottom of the fixture and the surface. Closer to 30 on an 8 ft ceiling, closer to 36 when the ceiling is taller.

Anywhere people actually walk under it, keep at least 7 ft of floor clearance to the lowest point. That is the number that stops a beautiful chandelier from becoming the thing everybody ducks.

For the fixture's own height, designers use about 2.5 to 3 in of fixture per foot of ceiling: roughly 20 to 24 in tall on an 8 ft ceiling, 25 to 30 in on a 10 ft one.

Number three

How many, and how far apart

Over a kitchen island, two pendants suit most islands and three suit a long one. For two, divide the island's length by four and set each pendant that far in from its end. For three, divide by three: one in the middle, the other two spaced from each end.

One long linear fixture is the other answer, and often the easier one: a single 47 in bar over a 7 ft island does the same job as three pendants with a third of the fuss, and nothing to line up.

Over a dining table

Pieces that fit the rule

Lumitierra Cielo

From $144.95

Rings of light in black or gold, in several diameters, so you can match the number above.

Lumitierra Olivo

From $98.95

Square or round, black or white, with adjustable color temperature.

Lumitierra Ribera

From $69.95

Multi-arm chandelier in 3, 6, 8 or 12 lights, with white or black shades.

Lumitierra Estela

From $101.95

Linear bar for a rectangular table, where a round fixture leaves the ends dark.

Over a kitchen island

One long bar, or a row of pendants

Lumitierra Brisa

From $227.95

47 in of clean light in one piece, instead of four recessed spots. Indoor only.

Lumitierra Astra

From $72.95

Small single pendant. The one to buy two or three of and space by the rule above.

Lumitierra Roble

From $320.95

A 24 in resin pebble, hung low over an island. Takes a standard E27 bulb.

For a stairwell or a two-story entryway

The room where the rule changes

In a double-height space the fixture is read from two floors, so it wants height rather than width. Hang the lowest point level with the second-floor landing, and keep the 7 ft clearance over the stairs themselves.

Lumitierra Vega

From $211.95

Long crystal pendant made for a stairwell drop.

Lumitierra Onda

From $379.95

Rotating pendant, round or elongated, with 6, 8 or 12 heads.

Before you buy

Worth knowing