For most photographic umbrellas used as light modifiers, the shaft is near the same length or slightly longer than the surfaces of the umbrella when they are collapsed.

Since the umbrella is measured straight across from one rim to the other and the umbrella itself is curved, the folded length will usually be a bit more than half the measured width.

For an umbrella 2 meters in diameter, the shaft will likely be a little longer than one meter.

It may be shorter, as many larger flash umbrellas also fold inside themselves as they collapse in much the same way that compact rain umbrellas meant to be carried in a purse or briefcase do.

This 34.5" (0.88 m) umbrella from B&H folds on itself as it collapses. Although the specifications with the product listing don't say what the folded length is, the listed box dimensions of 12 x 2.1 x 1.8 inches would indicate it is no longer than 12 inches (3 cm).

This 7' (2.1 m) Westcott is listed as 43.6" (1.1 m) when folded.

If you are willing to use a 60" (1.5 m) size, they're much more affordable and many fold down right to about 39" (1 m) long.

If the seller's listing doesn't give the folded dimensions of the item itself, the largest dimension of the box in which it is shipped will usually be very close to the length, and should never be less than the folded length.

Of course, if you are using a 1.5-2 meter umbrella, you probably also need to consider the folded dimensions of the stand you select to hold it.