Law of Cosines Calculator
Enter either:
- Two sides and included angle (to find third side)
- Three sides (to find one angle)
📐 Law of Cosines Calculator – Instantly Solve Any Triangle
Need to solve a triangle when the Law of Sines won’t cut it? Try our Law of Cosines Calculator! It handles any triangle—not just right-angled ones—and solves for unknown sides or angles with high accuracy. Fast. Free. No login required.
👉 Use the Law of Cosines Calculator
🔍 What is the Law of Cosines?
The Law of Cosines relates the lengths of a triangle’s sides to the cosine of one of its angles. It’s especially useful when:
- You know two sides and the included angle (SAS)
- You know all three sides (SSS) and want to find an angle
Law of Cosines Formula:
💡 When Should You Use the Law of Cosines?
Use this calculator when:
- The triangle is not right-angled
- You’re missing a side and have two sides + the included angle (SAS)
- You know all three sides and want to find an angle (SSS)
This is especially helpful when the Law of Sines doesn’t apply, such as with SSS or when angles are not opposite known sides.
⚙️ How to Use the Law of Cosines Calculator
Enter any one of these two valid input sets:
1. Solve for a missing side:
- Side a
- Side b
- Angle C (between a & b)
2. Solve for a missing angle:
- Side a
- Side b
- Side c
Output:
- If solving for a side: you’ll get the length of side c
- If solving for an angle: you’ll get angle C in degrees
✅ Instant results
✅ Handles decimals
✅ Simple, clean UI
🧮 Example: Find a Missing Side
Given:
Try it yourself in our calculator—no formulas needed!
💻 Why Our Law of Cosines Calculator Ranks #1
We built this tool with user experience and SEO in mind:
- 🎯 Precise & fast using JavaScript trig functions
- 📱 Mobile-friendly design
- 📘 Educational, not just functional
- 🌐 Free to use, no installs, no ads
Our calculator is ideal for:
- Students solving homework
- Teachers doing demos
- Engineers & architects working on site plans
- Anyone needing fast triangle math
🧠 FAQ: Law of Cosines Calculator
Q: Can it handle obtuse triangles?
A: Yes! It works with all triangle types, including obtuse and acute.
Q: What if I input values that don’t make a valid triangle?
A: The calculator checks for invalid inputs and will warn you when a triangle can’t be formed.
Q: Do I need to download an app?
A: No downloads! It runs entirely in your browser.
🚀 Ready to Solve a Triangle?
Whether you’re stuck on trigonometry homework or working on real-world geometry, our Law of Cosines Calculator is your go-to triangle solving tool.
