Mortgage CalculatorLoan CalculatorAuto Loan CalculatorCompound Interest CalculatorSimple Interest CalculatorSavings CalculatorRetirement CalculatorROI CalculatorCAGR CalculatorPresent Value CalculatorFuture Value CalculatorAnnuity CalculatorAPR CalculatorCredit Card Payoff CalculatorDebt-to-Income Ratio CalculatorIncome Tax Calculator (US Federal)Salary to Hourly Wage CalculatorTip CalculatorDiscount CalculatorSales Tax CalculatorProfit Margin CalculatorMarkup CalculatorBreak-Even CalculatorInflation CalculatorSavings Goal CalculatorExchange Rate CalculatorPercentage CalculatorPercentage Change CalculatorFraction CalculatorAverage CalculatorMean, Median & Mode CalculatorStandard Deviation CalculatorRatio CalculatorProportion CalculatorExponent CalculatorLogarithm CalculatorSquare Root CalculatorFactorial CalculatorGCD & LCM CalculatorPythagorean Theorem CalculatorQuadratic Equation CalculatorSlope CalculatorArea CalculatorPerimeter CalculatorVolume CalculatorCircle CalculatorTriangle CalculatorRandom Number Range AnalyzerScientific Notation CalculatorRounding CalculatorBMI CalculatorBMR CalculatorTDEE CalculatorCalorie CalculatorBody Fat CalculatorIdeal Weight CalculatorMacro CalculatorProtein CalculatorWater Intake CalculatorOvulation CalculatorPregnancy Due Date CalculatorConception CalculatorPeriod CalculatorPace CalculatorHeart Rate Zones CalculatorVO2 Max CalculatorOne Rep Max CalculatorSleep CalculatorBlood Alcohol Calculator (BAC)Lean Body Mass CalculatorCalories Burned CalculatorPregnancy Weight Gain CalculatorAge CalculatorDate Duration CalculatorDays Between Dates CalculatorAdd Days to Date CalculatorBusiness Days CalculatorWork Hours CalculatorTime Duration CalculatorTime Zone ConverterWeek Number CalculatorDay of Week CalculatorLeap Year CalculatorUnix Timestamp ConverterTime Add / Subtract CalculatorDays Until CalculatorZodiac Sign CalculatorChinese Zodiac CalculatorRetirement Date CalculatorQuarter CalculatorLength ConverterWeight ConverterTemperature ConverterVolume ConverterArea ConverterSpeed ConverterTime ConverterData Storage ConverterPressure ConverterEnergy ConverterPower ConverterForce ConverterTorque ConverterAngle ConverterFuel Consumption ConverterCooking ConverterShoe Size ConverterDensity ConverterFrequency ConverterHeight ConverterFlow Rate ConverterNumber to Words ConverterRoman Numeral ConverterBeaufort Scale ConverterScreen Size CalculatorDecibel ConverterConcrete CalculatorTile CalculatorPaint CalculatorFlooring CalculatorDrywall CalculatorBrick CalculatorGravel CalculatorMulch CalculatorDeck CalculatorFence CalculatorRoof Pitch CalculatorRoofing Material CalculatorStairs CalculatorSquare Footage CalculatorCubic Yard CalculatorBoard Feet CalculatorInsulation CalculatorWallpaper CalculatorOhm's Law CalculatorParallel Resistor CalculatorVelocity CalculatorAcceleration CalculatorKinetic Energy CalculatorPotential Energy CalculatorForce CalculatorMomentum CalculatorFriction CalculatorProjectile Range CalculatorPendulum CalculatorWavelength CalculatorpH CalculatorMolarity CalculatorDilution CalculatorIdeal Gas CalculatorBoyle's Law CalculatorHalf-Life CalculatorGPA CalculatorGrade CalculatorFinal Grade CalculatorWeighted Grade CalculatorDog Age CalculatorCat Age CalculatorElectricity Cost CalculatorFuel Cost CalculatorSplit Bill CalculatorUnit Price CalculatorReading Time CalculatorSubnet CalculatorDownload Time CalculatorProbability CalculatorRent Affordability CalculatorSolar Payback CalculatorHousehold Budget CalculatorEmergency Fund Calculator

Triangle Calculator

Triangle area from base and height, or area and perimeter from three sides (Heron).

By CalcHub Editorial · Last reviewed

Quick answer

  • Formula: Base–height: Area = (b × h) ÷ 2 · Heron: Area = √(s(s−a)(s−b)(s−c)), where s = (a+b+c) ÷ 2
  • Worked example — Area: 6.0000 (full example below).

Triangle Calculator

Worked example result
Area6.0000
Perimeter (three-sides mode)12.0000
Semi-perimeter (three-sides mode)6.0000

The 3-4-5 triangle: perimeter 12, semi-perimeter 6, and Heron's formula gives √(6 × 3 × 2 × 1) = √36 = 6 for the area — matching (3 × 4) ÷ 2 from the base–height method.

Diagram: how the Triangle Calculator works — you enter What do you know?, Base (base–height mode), Height (base–height mode), Side a (three-sides mode), Side b (three-sides mode), Side c (three-sides mode); it applies the formula Base–height: Area = (b × h) ÷ 2 · Heron: Area = √(s(s−a)(s−b)(s−c))…; and the worked example gives Area: 6.000
How the Triangle Calculator works — the inputs, the formula, and a worked example (Area: 6.0000).

There are two common ways to size a triangle. If you know the base and the vertical height, the area is half their product. If you know all three sides instead, Heron's formula finds the area from the sides alone — no height needed.

Choose the mode that matches what you know. In three-sides mode the calculator also returns the perimeter and semi-perimeter, and it checks the triangle inequality: the two shorter sides must together exceed the longest side, or no such triangle exists.

The formula

Base–height: Area = (b × h) ÷ 2 · Heron: Area = √(s(s−a)(s−b)(s−c)), where s = (a+b+c) ÷ 2

Worked example

The 3-4-5 triangle: perimeter 12, semi-perimeter 6, and Heron's formula gives √(6 × 3 × 2 × 1) = √36 = 6 for the area — matching (3 × 4) ÷ 2 from the base–height method.

Worked example for the Triangle Calculator: with What do you know? Three sides (Heron's formula), Base (base–height mode) 0, Height (base–height mode) 0, the result is Area: 6.0000; Perimeter (three-sides mode): 12.0000.
The worked example, with the example values entered and the results they give.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

Why can't I get a perimeter from base and height?

Because many different triangles share the same base and height but have differently slanted sides — sliding the apex sideways keeps the area identical while stretching the perimeter. Perimeter is only shown in three-sides mode.

What is the triangle inequality?

Any two sides of a triangle must add up to more than the third side. Sides of 2, 3 and 6 cannot form a triangle because 2 + 3 < 6 — the two short sides cannot reach each other, and the calculator flags this.

Category: Math calculators

Sources & methodology

This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.

Content last reviewed by CalcHub Editorial.

Embed this calculator on your site

Free to use with attribution — paste the snippet below and the calculator appears on your page, with a link back to CalcHub.

<iframe src="https://calc-hub-63e.pages.dev/embed/triangle-calculator" width="100%" height="640" style="border:1px solid #d9e2ea;border-radius:12px" loading="lazy" title="Triangle Calculator — CalcHub"></iframe>

Open the embed version →

Area Calculator — how-it-works diagram

Area Calculator

Area of a square, rectangle, circle, triangle, trapezoid, parallelogram or ellipse.

Math →
Pythagorean Theorem Calculator — how-it-works diagram

Pythagorean Theorem Calculator

Find the hypotenuse or a missing leg of a right triangle.

Math →
Perimeter Calculator — how-it-works diagram

Perimeter Calculator

Perimeter of squares, rectangles, triangles and regular polygons, plus circumference.

Math →
Circle Calculator — how-it-works diagram

Circle Calculator

Diameter, circumference and area from a circle's radius.

Math →