Last updated: October 22, 2026 · Written by the Math Made Easy math teachers
Looking for 6th grade volume rectangular prism? Then this Grade 6 lesson on Finding the Volume of Rectangular Prisms explains each idea step by step, with worked examples.
Quick answer: The volume of a rectangular prism is the number of unit cubes that fill it. Multiply length, width and height, V = lwh, or multiply the base area by the height, V = Bh. With fractional edges, pack with unit-fraction cubes or multiply the fractions. Answer in cubic units.
Standards: 6.G.A.2 · Level: Grade 6
What is volume, and how do unit cubes measure it?
Volume describes the room inside a solid. Measure it by counting identical cubes that fill the solid completely, leaving no gaps and no overlaps.
A unit cube is a cube measuring one unit on every edge, so it takes up 1 cubic unit. The volume of a solid equals the count of unit cubes inside it, reported in cubic units like in³, ft³ or cm³.
How do you measure volume when the edges are fractions?
Fill the prism with smaller cubes whose edge is a unit fraction, such as ½ or ¼. A cube with edges of ½ foot has volume ½ × ½ × ½ = 18 cubic foot. The prism below is 1½ ft by 1 ft by ½ ft, so it holds 3 × 2 × 1 = 6 of these cubes.
Total volume: 6 × 18 = 34 cubic foot. Multiplying the edges gives the same result: 1½ × 1 × ½ = 34.
What are the volume formulas for a rectangular prism?
V = l × w × h or V = B × h
B is the area of the base. Either multiply the base area by the height or multiply all three edges together.
- Write the length, width and height with the same unit.
- Choose V = lwh, or V = Bh if the base area is given.
- Multiply, using fraction or decimal multiplication as needed.
- Write the answer in cubic units.
A planter box is 2½ ft long, 1½ ft wide and ¾ ft deep. Find its volume.
V = 52 × 32 × 34 = 4516 = 2 1316 cubic feet.
Writing square units for volume, or adding the three edges instead of multiplying them. Volume is always cubic units.
Picture one layer first: base area tells how many cubes cover the floor. Then stack as many layers as the height says.
- Volume counts unit cubes and is measured in cubic units such as ft³.
- V = lwh and V = Bh give the same volume for a right rectangular prism.
- A cube with edge ½ has volume ⅛ cubic unit.
- All edges must use the same unit before multiplying.
Finding the Volume of Rectangular Prisms: frequently asked questions
What is a unit cube?
A unit cube has edges one unit long, so its volume is 1 cubic unit. Cubes with smaller edges, such as ½ foot, can also be used as a measuring unit.
Why is a cube with edge ½ foot worth ⅛ cubic foot?
Eight such cubes fit in a 1 foot by 1 foot by 1 foot cube, because 2 × 2 × 2 = 8. Each small cube is therefore one eighth of a cubic foot.
What does B mean in V = Bh?
B is the area of the base of the prism, found by multiplying two of its edges. The height h is the edge perpendicular to the base.
Can I multiply fractions to get volume?
Yes. Multiplying the three edge lengths works for whole numbers, fractions and decimals. The result matches counting unit-fraction cubes.
How do I find a missing edge when the volume is known?
Divide the volume by the product of the two known edges. For V = 180 with l = 9 and w = 5, the height is 180 ÷ 45 = 4.
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