This umbrella is made using black polyester on a stick with a
24" Frame and comes with a Malacca Handle. The length of this
umbrella is approximately 35" (89 cm) from handle to ferrule and
the cover when opened is approximately 48" in diameter (122
cm).
Interestingly Malacca wood was the most commonly used material
for swordsticks, so perhaps Mycroft's umbrella does in fact conceal
a blade inside, bearing in mind he carries it everywhere he
goes.