DIY Cost Tools
Rectangular Prism Calculator
MATH & GEOMETRY CALCULATOR
Find volume, total surface area, and space diagonal of a rectangular prism.
Use the same length unit throughout. All fields are required. Assumes a closed solid with straight edges. Thickness, seams, and material waste are excluded.
How to use this calculator
Enter your dimensions and select Calculate. Length results use your input unit, areas use its square, and volumes use its cube. Retain measurement precision until the final answer.
Formula and explanation
V = lwh; area = 2(lw+lh+wh); diagonal = √(l²+w²+h²)
A rectangular prism has six rectangular faces meeting at right angles.
Worked example
For Length (units) = 6, Width (units) = 4, Height (units) = 3, results are Volume (cubic units): 72; Surface area (square units): 108; Space diagonal (units): 7.8102497.
Important limitations
Assumes a closed solid with straight edges. Thickness, seams, and material waste are excluded.
Ideal geometry does not account for manufacturing tolerances or measurement uncertainty. This is a calculation aid, not a structural design or building-code approval. Absolute inputs must not exceed one trillion.
Frequently asked questions
Are all faces included?
Yes, including the top and bottom.
Which diagonal is shown?
The interior diagonal joining opposite corners.
Can I mix inches and centimeters?
Convert all lengths to one unit first. Mixed units produce incorrect results.
Why did my result disappear?
Blank, invalid, or out-of-range inputs clear the previous result and display an instruction.
Review notes
Reviewed October 1, 2026. Default results were checked against the displayed formulas. Script tests covered blank, negative, nonfinite, and excessive inputs. Results run locally in your browser.