Triangle Area Calculator
Calculate the area of a triangle using base and height, three sides, or two sides and the included angle.
Calculation Method
Triangle Dimensions
Calculator guide
Triangle Area Calculator
This triangle area calculator finds the area from a base and perpendicular height, three side lengths, or two sides with their included angle. Choose the input mode that matches the measurements you have, and keep all side lengths in the same unit.
How to use the calculator
- 1Select the available triangle method: base and height, three sides, or two sides with the included angle.
- 2Enter the measurements in consistent units. For the three-side method, the side lengths must satisfy the triangle inequality; for the angle method, use the angle between the two entered sides.
- 3Read the area result. The calculator displays a rounded value, so retain more precision if the measurement is being used in a later calculation.
Important details to understand
1.Start with the right inputs
Check every number, date, unit, and selected mode before calculating. A correct formula can still give a misleading answer when an input is missing, entered in the wrong unit, or based on a different time period.
2.Know what the calculation includes
The method below describes what this tool uses. Real situations can involve extra rules, costs, calendar conventions, or personal details that are not part of the form, so compare the assumptions with your actual question.
3.Read the unit and rounding
Look at the label as well as the displayed number. Rounding can change the last digits, and results in different units or time periods are not directly comparable until you convert them consistently.
4.Treat the result as a useful check
Use the output to understand a calculation, explore a scenario, or make an initial estimate. When a result affects a formal deadline, a health decision, a contract, or a large payment, confirm it with the relevant source or qualified professional.
How the calculation works
Base-height area is ½bh. With three sides, Heron's formula uses s=(a+b+c)/2 and area=√[s(s−a)(s−b)(s−c)]. With two sides and included angle C, area=½ab sin(C). These methods produce square units from the input length unit.
A worked example
For a base of 10 cm and perpendicular height of 6 cm, area = ½×10×6 = 30 cm². The height must meet the base at a right angle.
When this calculator is useful
Estimate triangular plots, panels, fabric sections, or geometry problems. For an irregular shape, divide it into triangles and add their areas, taking care not to overlap sections.
Planning ahead
Try a few realistic input values to see how a change in an amount, measurement, date, or rate affects the answer.
Learning the method
Follow the explanation and example to understand which inputs matter and how they are combined.
Checking your own work
Compare the result with a hand calculation, a worksheet, or a trusted source when you need an independent sense check.
Explaining a result
Keep the original inputs and units with the output so another person can understand what was calculated.
Tips for a more reliable answer
- Enter the values from the same source and keep units consistent throughout the calculation.
- Check that you selected the mode or option that matches the question you are trying to answer.
- Use the worked example to confirm you understand the inputs and the kind of result the tool returns.
- Save the inputs with the result so you can review or repeat the calculation later.
Limitations and assumptions
The base-height method needs a perpendicular height, not a sloping side. The two-side method needs the included angle. Real measurements and rounding create uncertainty, so this is not a substitute for a survey.
Every result depends on the information entered and the method described above. The calculator cannot confirm that the inputs are complete or that its assumptions match a particular provider, policy, location, body, or real-world situation.
Frequently asked questions
Does the height need to be perpendicular?
Yes. The height is the shortest perpendicular distance to the chosen base.
Can three side lengths form any triangle?
No. The sum of any two sides must be greater than the third side.
What unit is the result?
It is the square of the length unit used for the sides, such as cm² or ft².
Why might my result differ from another calculator?
Tools can use different assumptions, units, date conventions, included costs, or rounding rules. Compare the inputs and method descriptions before deciding that one result is wrong.
What should I check if the answer looks wrong?
Review the selected mode, each entered value, the units, and any optional fields. Then compare a simple example with the method described in this guide.
Can I rely on the result for an official or high-impact decision?
Use the result as an estimate or explanation and check the limitations listed for this tool. Confirm important decisions with the relevant official source or a qualified professional.