3-4-5 Rule Calculator

Professional right triangle calculator with support for side length validation, hypotenuse calculation, ratio conversion, and more.

Bug report

Browser execution mode: Your data is processed in your browser and is not uploaded to the server.

Speed and Stability: Processing speed depends on your device and browser. For large batch work, the desktop version may be more stable.

Loading tool, please wait...

If the online tool fails to load or run, try the desktop tool.https://tools.yikeaigc.com/

Tool Usage

Return to old version

Set unit, precision, and tolerance first, then enter side lengths or process in batch. For 3-4-5 layout, right-angle checks, hypotenuse calculation, and common Pythagorean triples. Batch files are read locally only. The UI shows the first 20 files; processing applies to all files.

Current unitm

Tolerance0.005

ModeCheck 3 sides

Batch records0

Settings

Confirm the unit, display precision, and tolerance first. Tolerance is used to decide whether measurements are acceptable.

Basic parameters Unit only affects display and tolerance meaning

Length unit

Result precision

Tolerance type

Tolerance

Length error is compared with “theoretical hypotenuse - measured hypotenuse”.

Batch output format

Batch header First row is header; skip when processing

Single calculation

Choose a calculation type, then enter known values. Results update with right-angle check, 3-4-5 ratio, area, perimeter, and angles.

Check 3 sidesThe longer side is automatically checked as the hypotenuse

Edge length a

Side b

Side c

Find hypotenuseFormula c = sqrt(a² + b²)

Leg a

Leg b

Find legKnown leg must be less than the hypotenuse

Known leg

Hypotenuse

Generate by 3-4-5Use an existing site length to derive full dimensions

Baseline type

Base value

Batch processing

Upload CSV/TXT files or paste multi-line data. After processing, results are generated with original file names; duplicates get numbers appended.

Batch calculation typeValidation mode: each line a,b,c

Calculation type

Batch ratio base

Output format

Upload fileSupports .csv and .txt; multiple files allowed

Click to select files, or drag files here Only the first 20 file names are shown; all files are read when processing starts.

No file selected.

Paste DataOptional; supports comma, Tab, semicolon, or pipe separators

Multi-line data

Instructions

Software Instructions

Set parameters: First choose the length unit, result precision, tolerance type, and allowable error. Tolerance is used to determine whether the measured three sides are acceptable.
Select a single calculation:
- Verify three sides: Enter three sides, and the system will automatically identify the hypotenuse and determine whether the triangle is close to a right angle.
- Find the hypotenuse: Enter the two legs to calculate the diagonal length.
- Find a leg: Enter the known leg and hypotenuse to calculate the other leg.
- Generate by 3-4-5: Generate the corresponding dimensions by scale factor, shorter leg, longer leg, or hypotenuse.
View results: Click “Start Calculation” to view the conclusion, error, ratio, area, perimeter, angles, and calculation steps. A triangle diagram will be displayed on the right at the same time.
Use examples: Click “Fill Example” to quickly load data such as 3-4-5 or 5-12-13 for checking the calculation method.
Batch processing: Upload a CSV/TXT file or paste multiple lines of data, then choose the calculation type and output format. When processing multiple files, results are exported using the original file names; duplicate names will have numbers appended.
Save and export: You can save commonly used unit, precision, and tolerance settings. Single results can be copied or downloaded, batch results can be exported as CSV, JSON, or TXT, and multiple files will be packaged for download.

FAQ

A: The 3-4-5 rule is a common integer ratio based on the Pythagorean theorem. When the three sides of a triangle are proportional to 3:4:5, the longest side is the hypotenuse and the two shorter sides form a right angle. It is often used for layout, carpentry framing, and site measurement.

A: Tolerance should be set based on the measuring tools, on-site dimensions, and project requirements. For small woodworking projects, use a smaller length tolerance. For construction layout, set it according to the drawings or construction requirements, or use a relative error percentage instead.

A: Both are Pythagorean triples and can form right triangles. 3-4-5 is convenient for quick layout, while 5-12-13 suits another type of side-length combination. The tool can verify any three sides and will also display the ratio deviation.

A: In three-side validation mode, enter a,b,c on each line; in hypotenuse mode, enter the two legs on each line; in leg mode, enter the known leg and hypotenuse on each line; in ratio generation mode, enter one base value on each line. You can check “First row is header.”

A: Being able to form a triangle does not mean it is a right triangle. The tool compares the sum of the squares of the two shorter sides with the square of the hypotenuse, or compares the theoretical hypotenuse with the measured hypotenuse error. If it exceeds the tolerance, it will prompt you to review it.

A: Yes. In “Generate by 3-4-5,” select the hypotenuse as the base, enter the hypotenuse length, and the tool will automatically calculate the scale factor and provide the two legs, area, and perimeter.