RC Slab Designer

Flexural design of reinforced-concrete slabs by NSCP 2015 / ACI 318-14 strength design (SI). Pick a mode — 1-Way, 2-Way (Coefficient), or DDM — enter your loads, span and material data, and the app gives the minimum thickness, the factored moments, the required steel area, the bar spacing, the temperature steel, and a worked solution with a section / panel sketch.

⭐ Free to use · Balance … EP

Design mode

One-way slab: bends in one direction; design a 1 m strip spanning the short way.

① Materials & cover

f′_c (MPa)

f_y (MPa)

Clear cover (mm)

Main bar diameter d_b (mm)

Effective depth d = h − cover − d_b⁄2. φ = 0.90 (slabs are tension-controlled).

② One-way slab

Clear span l_n (m)

Dead load DL (kPa)

Live load LL (kPa)

Support condition (sets h_min) Moment location / coefficient (M_u = C·w_u·l_n²)

Pick the ACI moment coefficient for the section you are designing. Sign is informational; |M_u| is used for the steel.

② Two-way slab — ACI Method 3 (coefficient method)

Short clear span L_a (m)

Long clear span L_b (m)

Dead load DL (kPa)

Live load LL (kPa)

Slab thickness h (mm)

Short direction — coefficients C_a

C_a,neg

C_a,pos,DL

C_a,pos,LL

Long direction — coefficients C_b

C_b,neg

C_b,pos,DL

C_b,pos,LL

Negative: M = C·w_u·L². Positive: M = C_DL·(1.2DL)·L² + C_LL·(1.6LL)·L². Short uses L_a, long uses L_b.

② Direct Design Method

Span l₁ (c–c, m)

Transverse l₂ (c–c, m)

Clear span l_n (m)

Dead load DL (kPa)

Live load LL (kPa)

Slab thickness h (mm)

Span position

M_o = w_u·l₂·l_n²⁄8. Longitudinal moments distributed per ACI; then split into column & middle strips.

🧱 Slab design

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Bars · thickness · spacing

Design summary

Worked solution

⚠️ Preliminary design only. This is a study aid. Thickness, moments, steel area and bar spacing are first-pass values per NSCP 2015 / ACI 318 strength design — confirm the slab with full analysis (serviceability, deflection, detailing, development length) and your governing code before construction.