Umbrella sizes: why the same umbrella has two numbers

The two numbers

Every canopy can be described two ways, and both are honest.

Arc follows the fabric. Lay a tape from one rib tip, over the top of the canopy, down to the opposite rib tip, and read what it says. It is the figure most umbrella brands print, because a canopy curves and the curve adds length.

Diameter ignores the curve. It is the width of the circle the open umbrella covers, the shadow it casts at noon, the space it takes on a café table.

Neither is marketing spin on its own. The problem is comparison. A 48 inch arc and a 48 inch diameter are different umbrellas, and only one of them tells you whether two people stay dry.

Our own catalogue shows the gap where a maker publishes both figures:

• Weatherman golf umbrella: 66 inch arc, 56 inch open diameter.
• Weatherman travel umbrella: 42 inch arc, 38 inch open diameter.

Roughly a 10 to 15 percent difference in both cases. That is the correction to apply mentally when a listing gives you one number and you want to know the other.

What the number means by type

Travel and compact

The open size matters less here than the closed size, because the whole point is that it disappears into a bag. Travel canopies cluster between 38 and 46 inches of arc, which covers one person and a shoulder bag, and nothing in this class covers two adults properly whatever the number says.

Closed length is the specification that decides whether you carry it. The models we list publish figures between 11.5 and 16 inches folded: a 16 inch umbrella is a fine umbrella and a poor handbag umbrella, and that distinction is invisible on a size chart that only gives canopy arc. How to choose a travel umbrella goes through the trade in detail, and purse-sized umbrellas is the short end of it.

Golf

Golf umbrellas run from about 62 to 68 inches of arc, and the size exists for a reason that has nothing to do with rain volume: it has to cover a person plus a bag, and it has to do that while somebody walks. In our catalogue, ShedRain's Vortex publishes 62 inches, GustBuster's Pro series 62, and Weatherman's golf model 66 arc and 56 diameter.

Anything under 60 inches marketed as a golf umbrella is a large rain umbrella with a straight handle. That is not an insult: a 58 inch canopy is easier to carry through a car park and just as dry over one person. It is only a problem if you expect it to cover the bag too. The golf umbrella roundup has the comparison.

Patio

Patio umbrellas are sized against the table rather than the person, and the rule is about overhang: roughly two feet past the table edge on every side. That makes the sizing arithmetic different from every other type, which is why it has its own page: what size patio umbrella do you need has the chart from two makers and the base weight each size needs.

Why bigger stops helping

Canopy area grows with the square of the width, and so does the force the wind puts on it. Doubling the arc does not double the load, it roughly quadruples it, and that load has to go through the ribs, the shaft and your wrist.

This is the practical ceiling on umbrella size. A larger canopy keeps more of you dry in still rain and becomes harder to hold in exactly the weather you bought it for. Vents help by letting a gust through rather than lifting the whole canopy, which is why most large umbrellas have them and most compact ones do not.

Measuring one you already own

Open it, lay it on the floor, and take both figures:

1. Diameter: tape straight across from rib tip to opposite rib tip, over the top but pulled flat, ignoring the curve.
2. Arc: tape along the fabric, following the curve from tip to tip.
3. Closed length: from the tip of the shaft to the end of the handle, with the umbrella furled.

The third one is the number nobody publishes on a size chart and everybody needs, because it decides which bag the umbrella lives in.

Questions people ask

What size umbrella covers two people?

Look for 54 inches of arc or more, and expect both people to get a wet shoulder anyway if there is any wind. Two people under one canopy is a compromise; two compact umbrellas usually beat one large one for walking.

Is umbrella size measured open or closed?

Both, for different purposes. Canopy arc and diameter are measured open. Folded length is measured closed and is the figure that decides portability.

What is a standard umbrella size?

There is no standard. Travel canopies run about 38 to 46 inches of arc, full-length rain umbrellas about 48 to 58, golf umbrellas about 62 to 68. Patio umbrellas are sized to the table instead.