Determine a preliminary metal joist spacing from framing width, area loads, joist capacity and deflection criteria.
Framing Layout
The calculator selects a preliminary spacing based on load capacity and layout limits. It is not a substitute for a complete joist design.
Applied Loads
Area loads are converted into joist line loads using the selected spacing. Joist self-weight is added separately.
Joist Capacity and Deflection
If section properties are supplied, the calculator also performs a simplified simply-supported bending and deflection screening at the selected spacing.
Ready to calculate preliminary joist spacing.
Preliminary Spacing Result
Recommended Preliminary Spacing
—
Capacity Spacing
—
maximum
Deflection Spacing
—
maximum
Layout Spacing
—
selected
Number of Joists
—
approx.
Line Load
—
kN/m
Spacing and Load Summary
Load Conversion
Dead load—
Live load—
Additional load—
Factored area load—
Joist self-weight—
Total line load—
Layout Planning
Total framing width—
Selected spacing—
Number of spaces—
Approx. joist count—
Actual equalized spacing—
Joist Spacing Screening
Check
Demand
Limit
Utilization
Status
Metal Joist Layout Preview
Floor / roof deck
Preliminary joist spacing
The illustration is a simplified framing-layout reference and is not a construction drawing.
Joist Line Load Formula
A joist supporting a uniformly distributed area load receives a line load based on its tributary width.
w = q × s + wj
Where q is the factored area load, s is joist spacing and wj is joist self-weight.
Capacity-Based Spacing
If an allowable joist line-load capacity is supplied, the preliminary capacity-controlled spacing is estimated from:
scapacity =
(C − wj) ÷ q
The resulting spacing is limited by the entered maximum practical spacing.
Deflection-Based Spacing
For a simply supported joist under a uniform line load, the preliminary midspan deflection is estimated using:
δ = 5wL⁴ / 384EI
The allowable deflection is:
δallow = L / Deflection Limit
The calculator solves the simplified relationship for a spacing that satisfies the entered deflection criterion.
Framing Layout Calculation
After selecting the preliminary maximum spacing, the calculator determines an approximate number of equal joist spaces across the framing width.
Number of Spaces = Ceiling(Framing Width ÷ Selected Spacing)
Actual Equal Spacing = Framing Width ÷ Number of Spaces
Equalizing the spaces avoids a final partial bay and provides a simple preliminary layout reference.
Important Limitations
This is a preliminary metal joist spacing calculator.
It does not select a joist section.
It does not perform complete joist strength design.
It does not check local buckling or distortional buckling.
It does not check lateral-torsional buckling.
It does not check web crippling or bearing.
It does not design joist connections.
It does not calculate bridging, blocking or bracing requirements.
It does not account for openings or concentrated loads.
It assumes simplified uniformly distributed loading.
It does not automatically select code-specific load combinations.
Actual allowable spacing depends on the selected joist profile, span, restraint, deck attachment, loading and applicable design standard.
Engineering warning: Use the result for preliminary framing layout only. Final metal joist spacing must be verified using the actual joist section, span, loading, restraint, connections and governing structural requirements.
Frequently Asked Questions
What does the Metal Joist Spacing Calculator calculate?
It estimates preliminary joist spacing from framing width, applied area loads, joist capacity and deflection criteria.
How is joist spacing related to load?
A wider joist spacing increases the tributary width and therefore increases the line load carried by each joist.
Does the calculator include joist self-weight?
Yes. An entered joist self-weight in kg/m is converted into a line load.
Does it check deflection?
Yes. If section properties and span are entered, the calculator performs a simplified simply-supported deflection screening.
Does it calculate the number of joists?
Yes. It estimates the number of equal framing spaces across the entered width and reports the resulting approximate joist count.
Can this be used for final construction spacing?
No. Final spacing requires complete member design and verification against the applicable structural standard and project conditions.