Free · Algebra and geometric models
Trapezoid Bases, Offsets, Angles and Measures
Relate bases, height, side offsets, legs, perimeter and area of a trapezoid.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
For the worked inputs, Area (A) = 20, Perimeter (P) = 20, Median = 5.
A=(a+b)h/2; P=a+b+c+d; a=left offset+b+right offset
Worked example
Enter these known values and leave the other values blank.
- Base (a)
- 8 cm
- Base (b)
- 2 cm
- Height (h)
- 4 cm
- Leg (c)
- 5 cm
- Leg (d)
- 5 cm
- Area (A)
- 20 cm²
- Median
- 5 cm
- Perimeter (P)
- 20 cm
- α
- 53.13 deg
- β
- 126.87 deg
- γ
- 126.87 deg
- δ
- 53.13 deg
Assumptions and limitations
- The longer base a strictly exceeds the positive shorter base b.
- Offsets are measured along the longer base and correspond to acute lower-base angles; the model describes an inset upper base.
Common questions
What must I enter?
Choose the mode when available and enter its independent known quantities. Leave an unknown editable quantity empty to use a supported inverse.
How should I use the result?
Interpret the numbers within the stated mathematical assumptions. Available unit selectors convert quantities; display rounding does not replace the internal calculation.
References
Explicit real-model bounds validate dimensions, inverse branches and discrete controls omitted or approximated in this capture. The international acre is exactly 43560 square international feet; Bookify replaces the rounded captured area factor.
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