Masonry Wall Design Calculator
Design reinforced masonry walls: check slenderness, compressive capacity, moment capacity, and load adequacy.
About this calculator
This calculator walks a CMU wall section through the two checks that govern whether it can carry an axial load safely: slenderness and compressive capacity. It first derives f'm, the assembly's compressive strength, by multiplying your block strength by a mortar-type factor (0.85 for Type M, 0.75 for Type S, 0.65 for Type N) as a simplified stand-in for the more detailed unit-strength tables in TMS 402. Slenderness is the wall's unsupported height divided by its thickness (h/t); a reduction factor then discounts capacity as that ratio climbs, using 1 − (h/140t)² for h/t up to 99, and a steeper (70/ratio)² falloff beyond that — the same shape as buckling curves for compression members generally. Net area assumes a standard 52% solid CMU cross-section rather than reading an actual unit's core geometry.
Compressive capacity then combines strength reduction factors (φ = 0.6, plus 0.80 for masonry), f'm, net area, and the slenderness factor; the wall passes if your applied axial load stays under that number. Moment capacity is reported separately from the reinforcing steel area and yield strength, but note that the "adequate" check only compares axial load against compressive capacity — it does not fold bending demand into the pass/fail flag, so a wall with unaddressed lateral moment could still show as adequate. Treat this as a preliminary sizing check, not a substitute for a stamped design against your project's actual code edition and unit properties.
Inputs
TMS 402: min 150 mm load-bearing; 200 mm (8") standard CMU; 300 mm (12") for high axial loads
ASTM C90 / TMS 402: standard CMU f'm 13–15 MPa; high-strength 20–30 MPa; min 13.8 MPa
Results
Compressive Capacity
555,153 N
Allowable Axial Load
555,153 N
Adequate?
1 (1=yes, 0=no)
How to Use This Calculator
- Enter the wall height, thickness, and the design wind pressure in psf.
- Input the masonry compressive strength (f'm) and the reinforcing steel yield strength.
- Set the axial load from floors or roof above in plf.
- Review the Moment Capacity, Shear Capacity, and the Combined Stress Check.
- Ensure unity ratios for bending and shear are both under 1.0 per TMS 402.
How the result changes with Wall Thickness
| Wall Thickness | Compressive Capacity | Allowable Axial Load | Adequate? |
|---|---|---|---|
| 100 | 267,906 N | 267,906 N | 1 (1=yes, 0=no) |
| 150 | 412,604 N | 412,604 N | 1 (1=yes, 0=no) |
| 300 | 838,102 N | 838,102 N | 1 (1=yes, 0=no) |
| 400 | 1,119,977 N | 1,119,977 N | 1 (1=yes, 0=no) |
What each input means
- Wall Height
- Unsupported height of the masonry wall between lateral supports.
- Wall Thickness
- Nominal thickness of the masonry wall per TMS 402 (Masonry Building Code). Standard CMU: 100 mm (4"), 150 mm (6"), 200 mm (8", most common), 250 mm (10"), 300 mm (12"). TMS 402 requires minimum 150 mm for load-bearing.
- Wall Length
- Length of wall section under consideration.
- Block Compressive Strength
- Compressive strength of the concrete masonry unit per ASTM C90. Standard CMU minimum f'm = 13.8 MPa (2,000 psi); high-strength CMU 20–40 MPa. Per TMS 402, f'm is the specified compressive strength of the assembly, typically 13–20 MPa.
- Mortar Type
- Mortar type per ASTM C270. TMS 402 specifies mortar by type.
- Rebar Spacing
- Center-to-center spacing of vertical reinforcing bars.
- Rebar Size (diameter)
- Nominal diameter of vertical reinforcing bars. Common: 10, 13, 16, 19 mm.
- Applied Axial Load
- Factored axial compression load applied to the wall section.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersWall Height = 3, Wall Thickness = 200, Wall Length = 1000, Block Compressive Strength = 15 = 8 input(s) provided
- Calculate Compressive CapacityCompressive Capacity555153 = 555153
- Calculate Allowable Axial LoadAllowable Axial Load555153 = 555153
- Calculate Adequate?Adequate?1 = 1
- Calculate Slenderness RatioSlenderness Ratio15 = 15
- Calculate Moment CapacityMoment Capacity12725984 = 12725984
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the calculator's Adequate? check ignore the Moment Capacity it reports?
The pass/fail flag only compares your applied axial load against compressive capacity — it never combines that with the moment capacity number shown alongside it. That means a wall carrying an out-of-plane bending demand (from wind or eccentric loading) could show 'adequate' here even though its actual combined stress state would fail a real interaction check. Treat the Moment Capacity output as a separate reference value, not something already folded into the yes/no result.
How does the mortar type I select change the wall's strength?
Mortar type sets the factor multiplied against your block compressive strength to get f'm: Type M (higher cement content, used below grade) gives the highest factor at 0.85, Type S gives 0.75, and Type N (common above-grade) gives 0.65. A weaker mortar factor directly lowers f'm, which then lowers both the compressive capacity and moment capacity outputs, so switching from Type N to Type M can meaningfully increase your allowable load without changing the block itself.
Why does increasing wall height hurt capacity even if the load stays the same?
Height feeds into the slenderness ratio (h/t), and this calculator applies a slenderness reduction factor that shrinks toward zero as that ratio climbs — using 1 − (h/140t)² up to h/t = 99, then a steeper (70/ratio)² falloff beyond it. A taller, thinner wall is more prone to buckling under axial load, so the same block and mortar can support far less load once the unsupported height grows relative to thickness.
Does this calculator account for the actual hollow geometry of my CMU block?
No — it assumes a fixed 52% solid cross-section as a stand-in for real block core geometry, rather than reading the specific unit's net area from a manufacturer's data sheet. If your actual CMU has a different percent-solid (common for specialty or high-strength units), the net area, compressive capacity, and moment capacity here will all be approximations rather than exact figures.
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