Three sides (SSS)
Side a + Side b + Side c
s = (a+b+c)/2; A = √[s(s−a)(s−b)(s−c)]
Open calculator ↗GEOMETRY, ONE FIGURE AT A TIMETriangle.
Triangle.
Understand every measure.
Three sides, many ways to solve. Four free tools, clear formulas and a little discovery along the way.
Find your calculator ↗FIGURE 022D / REFERENCE DRAWING
TRIANGLENOT TO SCALE
THE CALCULATOR DESK
Start with what you know.
4 calculators available
Base and perpendicular height
Base b + Perpendicular height h
A = bh/2
Open calculator ↗Two sides and included angle
Side a + Side b + Included angle θ
c² = a²+b²−2ab cos θ; A = ab sin θ/2
Open calculator ↗Third interior angle
Angle α + Angle β
γ = 180°−α−β
Open calculator ↗MEET THE FIGURE
A triangle, explained.
A triangle is a plane polygon bounded by three straight sides. Its vertices determine three interior angles. A valid non-degenerate triangle has positive area, and the sum of its two shorter sides must exceed the longest side.
Understand the properties ↗LOOK A LITTLE CLOSER
More than a formula.
A triangle is rigid when its three side lengths are fixed, which helps explain triangular bracing.
The included angle in SAS lies between the two entered sides. A sloping side is usually not the perpendicular height.
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.