How to use the trapezoid volume calculator
- Choose Trapezoid prism if you know the two parallel sides, or Trench or ditch if you know the bottom width, depth and side slope.
- Enter the dimensions and pick the unit for the cross section.
- Enter the length and its unit. The two units can differ, for example metres and feet.
- Read the volume in cubic metres, litres, cubic feet, cubic yards and US gallons.
Worked examples
What is a side slope?
A side slope of 1.5 to 1 (written 1.5H:1V) means the bank moves 1.5 units sideways for every 1 unit it goes down. A slope of 0 gives vertical walls, which makes the trench a rectangle. Steeper slopes have a smaller number.
Frequently asked questions
What is the volume formula for a trapezoid?
A flat trapezoid has no volume, only area. For a solid with a trapezoid end, the volume is the trapezoid area times the length: V = (a + b) / 2 x h x L.
Is the height the slanted side?
No. Height is the straight distance between the two parallel sides. If you only know the slanted length, use the trench mode or work out the height first.
Can one base be zero?
Yes. If one base is zero the end face is a triangle and the formula still works. At least one base must be above zero.
How do I convert the result to litres or gallons?
One cubic metre is 1,000 litres. The tool also shows US gallons. Multiply cubic metres by 264.172 to get gallons.
Does it calculate the soil to be dug out?
Yes, the volume is the amount of material removed from a trench with these dimensions. Loose soil takes up more space than soil in the ground, so allow extra for hauling.