Triangle Calculator
Solve the triangle you know.
Triangle inputs
Choose the measurements you actually know.
Each method retains its own source values; only active fields are validated.
Source, angle and output choices
Enter all three sides. A nondegenerate triangle must satisfy every strict triangle inequality.
Use a finite decimal, scientific e notation or an integer fraction.
Use a finite decimal, scientific e notation or an integer fraction.
Use a finite decimal, scientific e notation or an integer fraction.
The source unit interprets all known side, base and height values together.
Converts all solved sides, perimeter, altitudes, medians and circle radii.
Coverage converts independently, including international acres and hectares.
Exact SSS radicals stay unchanged. Numerical trigonometry uses at most ten decimal places; very small nonzero values retain scientific views.
Sources support sixty significant decimal digits or sixty digits per fraction integer, one hundred eighty characters and scientific exponents from negative one hundred through positive one hundred. Exact squared magnitudes have an eighteen-hundred-digit limit. Trigonometry uses normalized numerical calculations with explicit side-ratio, angle and near-tangent limits. See the guide for these boundaries.
Interpreted active measurements
Triangle solution: triangle area
Scalene, right
Rounded area view
Perimeter
Semiperimeter
Solved triangle diagram
Calculation step by step
Interpret the active source
Lowercase sides are opposite matching capital-letter angles. Only this method's active measurements are used.
Solve the selected triangle method
The strict triangle inequality is checked exactly before Heron's formula. Rational source strings and verified radicals remain exact.
Read coverage and boundary separately
Perimeter is a length; coverage is an area. Output selectors convert them independently using exact physical unit definitions.
Derive altitudes, medians and circle radii
The same recovered triangle defines every additional quantity. In SSS mode, squared radical certificates preserve exact values; bounded simplification does not promise complete arbitrary factorization.
All triangle result details
Exact SSS values retain verified squared magnitudes. Trigonometric solutions and all angle views are numerical approximations. The rounded column never becomes a new source.
| Quantity | Exact or numerical value | Rounded view | Interpretation |
|---|---|---|---|
| Side | Opposite the matching capital-letter angle. | ||
| Side | Opposite the matching capital-letter angle. | ||
| Side | Opposite the matching capital-letter angle. | ||
| Perimeter | Sum of all three boundary lengths. | ||
| Semiperimeter | Half the perimeter in output length units. | ||
| Triangle area | Coverage uses the independent output area unit. | ||
| Altitude to side | Perpendicular distance to the line containing this side. | ||
| Median to side | Connects the opposite vertex to the side midpoint. | ||
| Altitude to side | Perpendicular distance to the line containing this side. | ||
| Median to side | Connects the opposite vertex to the side midpoint. | ||
| Altitude to side | Perpendicular distance to the line containing this side. | ||
| Median to side | Connects the opposite vertex to the side midpoint. | ||
| Incircle radius | Radius of the circle tangent to all three sides. | ||
| Circumcircle radius | Radius of the circle through all three vertices. | ||
| Angle | Trigonometric angle view is numerical, including in exact SSS mode. | ||
| Angle | Trigonometric angle view is numerical, including in exact SSS mode. | ||
| Angle | Trigonometric angle view is numerical, including in exact SSS mode. |
Perimeter in all length units
| Unit | Exact or numerical value | Rounded view |
|---|---|---|
| Nanometers | ||
| Micrometers | ||
| Millimeters | ||
| Centimeters | ||
| Decimeters | ||
| Meters | ||
| Decameters | ||
| Hectometers | ||
| Kilometers | ||
| Mils (one thousandth inch) | ||
| Inches | ||
| International feet | ||
| International yards | ||
| International miles | ||
| International nautical miles | ||
| Typographic points (one seventy-second inch) | ||
| Typographic picas (one sixth inch) |
Triangle area in all area units
| Unit | Exact or numerical value | Rounded view |
|---|---|---|
| Square nanometers | ||
| Square micrometers | ||
| Square millimeters | ||
| Square centimeters | ||
| Square decimeters | ||
| Square meters | ||
| Square decameters | ||
| Square hectometers | ||
| Square kilometers | ||
| Square mils (one thousandth inch) | ||
| Square inches | ||
| Square international feet | ||
| Square international yards | ||
| Square international miles | ||
| Square international nautical miles | ||
| Square typographic points (one seventy-second inch) | ||
| Square typographic picas (one sixth inch) | ||
| International acres | ||
| Hectares |
Inputs saved with this calculation
- Method
- Three sides (SSS)
- Active source strings
- Side a: 3; Side b: 4; Side c: 5
- Source unit
- Centimeters
- Output length unit
- Centimeters
- Output area unit
- Square centimeters
- Angle convention
- degrees
- Rounded decimal places
- 6
Turn known measurements into a coherent triangle
Solve the case your measurements actually define
Choose the solving method from the relationships in the given problem. Three sides establish a unique shape up to reflection when all strict inequalities hold. An included angle requires a different approach from a non-included angle. The interpreted source keeps those relationships visible, while independent method buffers let you compare cases without overwriting another problem with unrelated measurements.
Recover distances and coverage from one figure
A complete solved triangle supplies coverage, perimeter, semiperimeter, perpendicular altitudes, medians, incircle radius and circumcircle radius. Side-based calculations retain exact rational and verified radical values rather than rounding an area and reusing it in later formulas. Angle-based methods identify numerical approximations honestly. The separate area-only workflow prevents an unrelated base and height from being labelled as another measurement of the same triangle.
Compare both ambiguous configurations
A non-included-angle source can describe two geometrically different triangles with identical given measurements. Inspect each branch and its opposite-side labels before applying additional practical constraints. The solver does not silently discard the supplementary inverse-sine candidate. Exported working preserves the complete solution set, while impossible or unresolved boundary cases receive a message instead of a plausible-looking invented diagram.
Triangle formulas and step-by-step examples
Check the three given sides
For , and , every pair sums to more than the remaining side. The perimeter is and the semiperimeter is . Heron coverage is . These exact relationships use the original source values rather than rounded intermediate measurements.
Derive other distances from that same triangle
The altitude to side is and its median is . An altitude reaches a side line perpendicularly, while a median reaches its midpoint. The incircle radius is and the circumcircle radius is . These relationships describe different constructions even when symmetry sometimes makes their lengths equal.
Distinguish included and opposite angles
Sides , and included angle define an SAS problem. The cosine law determines the missing side. Two known angles instead leave a third through , and opposite-side sine ratios then recover missing lengths. Preserve the specified side: the ASA side lies between the known angles, while the AAS side is opposite a stated known angle.
Retain both ambiguous branches
For , and non-included angle , the sine ratio is . Both the principal candidate and its supplement leave positive third angles. With opposite side , they meet at the tangent case . With opposite side , the sine ratio exceeds one and no triangle satisfies the given measurements.
Separate base-height coverage and dimensions
An independent base and perpendicular height give , but do not describe the default SSS triangle. The default perimeter converts to and its area to . Coverage needs a squared conversion factor; applying only a length factor gives the wrong magnitude and dimension.
Why the method, precision and source labels matter
The geometry is checked before it is drawn
- Strict exact inequalities separate valid SSS data from collapsed and impossible figures.
- Opposite-side labels and included-angle meanings stay visible in the interpreted source.
- Both SSA branches are checked, with special exact tangencies distinguished from unresolved numerical boundaries.
- A base and height define coverage only, without an unsupported perimeter or unique outline.
The mathematical record remains inspectable
- Rational side sources and verified radicals stay available beside separately rounded views.
- Normalized numerical calculations are checked against angle sums and cosine-law residuals.
- Seventeen length definitions and nineteen area definitions convert dimensions independently.
- Ordered equations, source records, complete tables, sharing, CSV and PDF preserve the assumptions behind the answer.
Triangle reasoning for study, teaching and measured sketches
Students connecting a formula to a labelled problem
Identify the known side-angle pattern before choosing a law. Compare exact three-side working with a numerical trigonometric solution to understand which quantities depend on approximation. The default right triangle offers independently checkable area, altitude and circle-radius relationships. Ambiguous and impossible examples demonstrate why an inverse-trigonometric result is a candidate that still needs geometric filtering.
Teachers preparing complete solution comparisons
Use one source record to explain opposite-side notation, included angles and the supplementary branch in SSA. The diagram follows actual solved vertices and uses equal physical axis scales. A reflected drawing represents the same measurements. Printed working retains both valid branches, while fractional, equilateral, tangent and area-only examples provide useful contrasts without mixing unrelated geometric models.
People checking idealized flat triangular dimensions
Convert a coherent set of measured lengths into useful output units while preserving their geometric roles. Check whether a height is perpendicular and whether an angle lies between the measured sides. Practical layouts can supply an additional constraint that selects one ambiguous branch. Curved surfaces, measurement uncertainty, material thickness, allowances and purchasing increments need additional models beyond an ideal plane triangle.
How it works in three quick steps.
Match the method to the known measurements
Choose three sides, two sides and their included angle, two angles with a stated side, or two sides and a non-included angle. Follow the opposite-side labels before entering numbers. Use base and perpendicular height only when coverage alone is defined. Select a shared source length unit and choose the angle convention explicitly.
Inspect every valid triangle and its working
Read the validity message before using a number. Strict triangle inequalities filter three-side inputs. A non-included-angle source can define no triangle, one triangle or two triangles, so inspect both valid branches. Side-based working retains verified radicals. Numerical trigonometry reports conditioning limits rather than forcing an unresolved boundary into a definite answer.
Convert dimensions and preserve the complete record
Choose independent output length and area units. Compare the solved sides, angles, perimeter, coverage, altitudes, medians and circle radii. The equal-scale drawing belongs to the inspected solution, with thin outlines omitted explicitly. Download every solution and conversion as CSV, share the active source or print both ambiguous branches to a PDF.
Save the complete problem and its solutions
Download every solution and conversion
CSV contains active source strings, unit choices, angle convention, every solved quantity, ordered equations and complete conversion values. Hidden conversion tables remain included, and ambiguous branches have separate solution labels. Exact squared magnitudes identify side-based radical values independently of display formatting. Preserve this record instead of copying a rounded area without its original side-angle interpretation and numerical assumptions.
Print readable mathematical working
Browser printing removes editing controls, includes both valid branches and preserves available equal-scale diagrams with their captions. Tables repeat their headings across pages and keep individual rows together. Choose a practical paper orientation when saving a PDF. Very long expressions use a visible notice pointing to the full CSV, keeping the printed record legible while complete numerical values remain downloadable.
Share one complete active problem
A shared fragment stores the selected method, its required measurements, angle convention and source/output units. Inactive editor buffers are excluded. Malformed, duplicated and extra imported fields are rejected, so another person receives a reproducible active problem. The first valid branch is inspected initially and all other branches remain available. Plain copying preserves readable mathematics for documents without a visual formula renderer.
Frequently Asked Questions
Which measurements can solve a triangle?
Why does SSA sometimes give two answers?
What do the side and angle letters mean?
Which results are exact in SSS mode?
Why are flattened triangles and zero sides rejected?
Does base-height coverage describe the SSS triangle?
How do degrees, radians and pi-radians differ?
What numerical limits apply to trigonometric methods?
Why are length and area output units independent?
Can I export and print both ambiguous solutions?
About this complete triangle calculator
This triangle calculator treats geometry as a defined set of connected measurements rather than a collection of unrelated formulas. The selected method identifies which sides and angles are known and how they meet or oppose one another. Three-side, included-angle, two-angle and non-included-angle problems therefore remain separate even when some numbers happen to match. The interpreted source and opposite-side labels preserve meaning, and the validity message states whether the data defines a triangle, two possible triangles, no triangle or coverage alone.
The side-based engine interprets finite decimal and integer-fraction entries as rational values. Strict inequalities are checked before coverage is calculated, while verified radical certificates preserve derived distances and area. Numerical angle views remain separate from exact expressions. Trigonometric workflows use normalized floating-point calculations with explicit conditioning limits, and accepted solutions are checked against angle-sum and cosine-law relationships. The tool does not claim arbitrary precision for inverse trigonometry or silently force a nearly tangent case into a misleading definite answer.
Every secondary measurement belongs to the same recovered triangle, including its altitudes, medians and the radii of its incircle and circumcircle. Independent output selectors keep lengths and coverage dimensionally clear. Base-height coverage has a deliberately narrower interpretation because those two measurements cannot determine a unique perimeter or outline. The diagram, source record, ordered equations, exact or numerical labels and complete exports preserve these assumptions for learning and later inspection. Extreme numerical limits and omitted thin outlines are explained alongside the result.
Who maintains this page
Ownership and review
Written and maintained by the Toolarithm editorial team. No review date is shown without a maintained editorial record. No independent professional review is claimed.
Methodology
Equations are checked by substituting worked examples into the stated relationship and comparing the result with the interactive implementation.
Read the editorial methodologyDates and sources
Review dates change only after a substantive method or content check.
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