三角形面積計算器
計算三角形的面積。
Calculating the Area of a Triangle
Overview
The area of a triangle is the space enclosed by its three sides. Depending on what you know — base and height, or all three sides — different formulas apply. This calculator computes the area instantly in your browser using the right method for your inputs.
How to Use (Step by Step)
- 1
Choose your known values
Enter base and height, or all three side lengths.
- 2
Calculate
The tool applies the matching formula automatically.
- 3
Read the area
The enclosed area is shown in square units.
How It Works
With a base and height, area = ½ × base × height. When you know all three side lengths instead, the tool uses Heron's formula: compute the semi-perimeter s = (a + b + c) ÷ 2, then area = √(s(s−a)(s−b)(s−c)). Both give the same area; the tool picks the formula that matches the measurements you provide.
When to Use This
Finding the area of a triangular plot or surface. Solving a geometry assignment. Calculating material for a triangular shape in a project.
Frequently Asked Questions
The tool uses Heron's formula, which finds the area from the three side lengths without needing the height.