In British English, an isosceles trapezoid is also known as isosceles trapezium. The base angles of an isosceles trapezoid are congruent. In Isosceles trapezium, the two parallel lines or sides are called as the bases and the two non parallel sides (other than the bases) are called as the legs. Here is an online Legs of an Isosceles Trapezoid calculator which helps to calculate the Leg Length of an Isosceles Trapezium using the given Perimeter, Base 1 and Base 2 values.
An isosceles trapezium with base lengths 8 and 10 cm has a perimeter of about 25 cm.
Leg Length = (perimeter - base1 - base2)/2
= (25 - 8 - 10) / 2
= 3.5 cm