Triangle Calculator: Fast and Friendly Tool

Use this triangle calculator to find perimeter, area, angles, and sides. It suits class work, design, and quick checks. Enter your values and see clear results in seconds.

How to Use This Tool

You have two input choices. Enter three sides, or enter two angles and one side. Pick the method that fits your data.

Using the Side Lengths Option

Fill these fields with positive numbers.

• Side A length
• Side B length
• Side C length
• Use one measurement unit for all sides

Follow these steps.

1. Type all three side lengths
2. Click Calculate from Sides
3. Read the perimeter, area, all angles, and triangle type

Example that works well.

• Sides 3, 4, and 5 produce a right triangle

Using the Angles and One Side Option

Enter two angles in degrees, and the side between those angles.

• First angle in degrees
• Second angle in degrees
• Known side length between those two angles

Follow these steps.

1. Enter the two angles that touch the known side
2. Enter the length of that side
3. Click Calculate from Angles
4. See the third angle, all sides, perimeter, and area

Example that fits this mode.

• Angles 60° and 60° with side 5 give an equilateral triangle

Why Use This Triangle Calculator?

This triangle calculator saves time and cuts guesswork. It works with any unit and gives clear labels. Students and pros use it for checks and quick planning.

Here is what the results mean.

• Perimeter adds the three sides
• Area shows square units based on your side unit
• Angles show in degrees with two decimal places
• Sides list in your input unit with two decimal places
• Triangle Type shows side class and angle class

Common uses include these cases.

• Check a homework triangle fast
• Plan a cut for a frame or panel
• Confirm survey angles on a site
• Validate a model in code or notes

Step-by-Step Guide

Step 1: Choose Your Method

• Pick Side Lengths if you know three sides
• Pick Angles and One Side if you know two angles and the side between them

Step 2: Fill in the Details

For Side Lengths

1. Enter side A as a positive number
2. Enter side B as a positive number
3. Enter side C as a positive number
4. Use one unit for all sides

For Angles and One Side

1. Enter angle one in degrees
2. Enter angle two in degrees
3. Enter the length of the side between those angles
4. Make sure the two angles add to less than 180°

Step 3: Hit Calculate

If you chose Side Lengths

1. Click Calculate from Sides
2. Review perimeter, area, angles, and triangle type

If you chose Angles and One Side

1. Click Calculate from Angles
2. Review the third angle, all sides, perimeter, and area

Read these notes for clean results.

• All inputs stay positive
• Angles use degrees
• For sides, any two sides sum to more than the third
• For angles, the two angles sum to less than 180°
• Use one unit for sides to keep the area correct
• Results round to two decimals
• Near equal sides or angles may change the type label

Technical Peek

The side mode uses Heron’s formula for area. It first computes the semiperimeter, which is half the perimeter. It then finds area from that value. It finds angles with the law of cosines for stable results.

The angle mode uses the law of sines to get the two missing sides. It sets the third angle to 180° minus the two given angles. It then computes area from two sides and the included angle using the sine rule.

Classification follows standard rules. Equal sides within a tiny margin read as equilateral or isosceles. One angle near 90° reads as a right triangle. A largest angle over 90° reads as obtuse. All angles under 90° read as acute.

Your New Best Friend in Math

Keep this triangle calculator close for fast checks. It turns raw inputs into clear values with no fuss. Use it for study, for work, and for quick sanity checks.

Start with one example, then plug in your own figures. Clean inputs give clean outputs, and you get answers you can trust.