Two semi-axes
Semi-major axis a + Semi-minor axis b
A = πab; e = √(1−b²/a²)
Open calculator ↗GEOMETRY, ONE FIGURE AT A TIMEEllipse.
Ellipse.
Understand every measure.
Two axes shape an elegant curve. Four free tools, clear formulas and a little discovery along the way.
Find your calculator ↗FIGURE 122D / REFERENCE DRAWING
ELLIPSENOT TO SCALE
THE CALCULATOR DESK
Start with what you know.
4 calculators available
Full axis lengths
Major axis length + Minor axis length
a = major axis/2; b = minor axis/2
Open calculator ↗Area and semi-major axis
Area A + Semi-major axis a
b = A/(πa)
Open calculator ↗Semi-major axis and eccentricity
Semi-major axis a + Eccentricity e
b = a√(1−e²)
Open calculator ↗MEET THE FIGURE
A ellipse, explained.
An ellipse is the set of points whose distances to two fixed foci have a constant sum. Its semi-major axis a is at least its semi-minor axis b. Full axis lengths are 2a and 2b.
Understand the properties ↗LOOK A LITTLE CLOSER
More than a formula.
A circle is an ellipse with coincident foci and equal axes.
Semi-axes are half the full axis lengths. The approximation label applies to perimeter, not to the area formula.
Explore three geometry facts ↗These tools use ideal Euclidean geometry. Every input must use the same unit. Numerical results are rounded and do not replace measurement, specialist design or safety checks. See worked examples.