Entered ratioPreliminary only
Span-to-Depth
Ratio Worksheet
Apply a ratio already selected for the exact system, support condition, material, edition, and project purpose.
Preset ACI and material ratios removed
The former page presented selected table values and broad steel/timber heuristics as universal choices. Applicability and modification conditions cannot be established from span alone.
Who it's for: structural engineers applying a documented span-to-depth ratio at schematic design, once the ratio and support condition are selected.
Preliminary depth
span ÷ entered ratio
Entered-ratio resultpreliminary
Depth in span units
—
—
—
How to use this calculator
1
Select the ratio outside the worksheet
Use the governing standard, manufacturer table, validated office method, or engineer judgment for the exact system.
2
Confirm the span definition
Clear span, centerline span, and effective span are not interchangeable.
3
Enter matching values
The output uses the same unit as the span.
4
Perform full design
Check strength, stability, vibration, short- and long-term deflection, fire, detailing, and constructability separately.
The formula
Preliminary depth = entered span ÷ entered ratio denominator.
Worked example
Example
A documented L/16 preliminary ratio applied to a 6,000 mm span gives 375 mm. The result does not establish a code minimum or adequate member.
When this estimate will be off
- Does not select or validate a ratio.
- Does not establish code minimum thickness or waive any analysis.
- Does not evaluate loads, strength, stability, vibration, deflection, fire, detailing, or adequacy.
Frequently asked questions
A common mistake: Does not select or validate a ratio.
The page could not determine the exact edition, member classification, support condition, material parameters, modification factors, or whether the table applied.
Sources
- User-selected governing or documented method — must establish the entered ratio and applicability
This free Structural Depth-to-Span Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.