Rectangular Duct Surface Area Calculator
Calculate a simple hvac quantity from your measurements. Review units, selected allowances and scope limits before using the result.
Rectangular Duct Surface Area
Starting values are illustrative. Replace them with your drawing measurements and selected allowances.
Calculated quantity
Formula: 2 × (width + height) ÷ 12 × length × (1 + allowance ÷ 100)
Straight rectangular duct lateral surface only. Excludes fittings, ends, seams, supports and insulation thickness effects. This is a quantity calculation; it does not supply a price, labor estimate or design approval.
For a drawing-based bid package, review the hvac estimating scope. Identify the current plan issue, included assemblies and required quantity or priced output. Confirm rates, exclusions and revisions separately from this planning calculation.
Prepare the Inputs
Use dimensions from the current drawing revision and match the units shown beside each field. Replace every illustrative starting value with your project inputs. The allowance is entered by you; there is no automatic industry-wide waste factor.
Review the Result
This tool calculates the displayed quantity only. It does not create a complete takeoff, price materials, calculate labor or approve a construction design. Measure different systems and assemblies separately and reconcile details that sit outside the formula.
Download a blank hvac quantity schedule, review hvac estimating scope or request a project quote.