What Is the Midsegment of a Trapezoid?
The midsegment of a trapezoid — also called the median or midline — is the line segment that connects the midpoints of the two non-parallel sides (the legs). A key property of this segment is that it runs parallel to the two bases and its length is exactly the average of those two bases. This calculator computes that length for you in one step.
How to Use This Calculator
Enter the length of the first parallel side (base a) and the length of the second parallel side (base b) in the same units. Click calculate and the tool returns the midsegment length m. The result table also echoes your inputs so you can verify them at a glance.
The Formula Explained
The governing equation is $$m = \frac{\text{Base }a + \text{Base }b}{2}$$ Because the midsegment sits exactly halfway between the two parallel bases, its length is the arithmetic mean of those bases. The formula is independent of the trapezoid's height or the lengths of its slanted legs — only the two parallel sides matter.
Worked Example
Suppose a trapezoid has a longer base of 10 cm and a shorter base of 6 cm. The midsegment is $$m = \frac{10 + 6}{2} = \frac{16}{2} = 8\text{ cm}$$ So a line drawn across the midpoints of the legs would be 8 cm long.
FAQ
Does the height affect the midsegment? No. The midsegment length depends only on the two parallel bases, not the height or leg lengths.
Can I use this for a parallelogram? Yes. In a parallelogram both bases are equal, so the midsegment equals either base.
What units does it return? The midsegment is returned in the same units you enter the bases in — keep both inputs consistent.
