NSCP One-Way Slab Thickness Calculator Philippines — Section 407 Complete Reference
NSCP 2015 (7th Edition) Section 407 — One-Way Slabs — governs every solid slab in the Philippines that spans in a single direction: floor slabs on beams, roof slabs, cantilevered balconies, and any slab where the long side is more than twice the short side. This page covers the section in full — the deflection-exempt minimum thickness table, the modifiers for non-standard fy and lightweight concrete, minimum flexural reinforcement, minimum shrinkage and temperature steel, and every spacing and detailing rule — with a calculator up front that runs the sizing path engineers actually use on 90% of projects: pick your span and support condition, get a code-compliant thickness, minimum steel area, and bar spacing instantly.
What this calculator sizes. The reinforcement mat and slab thickness set here — bar spacing, minimum steel ratio, cover — is exactly what NSCP 2015 Section 407 governs. Photo: AEDO Construction one-way slab reinforcement, ready for pour.
Implements NSCP 2015 (7th Edition), Section 407 — One-Way Slabs, in full: 407.3 (thickness), 407.4 (required strength), 407.5 (design strength), 407.6 (reinforcement limits), and 407.7 (reinforcement detailing). This calculator sizes non-prestressed slabs — the case covering nearly all residential and light-commercial construction in the Philippines. Prestressed-slab provisions are quoted for completeness where they occur in the code but are not computed here.
Which Span Is "L"? Short Side or Long Side?
This trips up almost everyone the first time: L is the span the slab actually bends across in one direction — for a rectangular panel supported on all four sides, that is the short side, because a one-way slab only qualifies as "one-way" when the long side is at least twice the short side (long/short ≥ 2), and nearly all the load travels the short way. If your slab spans directly between two parallel beams or walls with no support on the other two edges, there's no ambiguity — L is simply that span.
Support Conditions Illustrated
Click a diagram below to load that support condition straight into the calculator. The dashed line in each sketch is the deflected shape — it shows why continuity (a slab that carries negative moment into an adjacent span) lets you build thinner than a simple span, and why a cantilever needs the thickest section of all.
Diagrams are schematic (elevation/section view) — solid gray = slab, dashed blue = deflected shape, hatch blocks = continuous or fixed supports, triangle/circle = simple pin/roller supports.
Typical Reinforcement Layout — Plan View (Top View)
The elevation sketches above show behavior; this is what actually gets drawn on a structural plan. Two adjacent bays of a one-way slab, both ends continuous, viewed from above — main bars run the short (spanning) direction, dropping to the bottom of the slab at midspan and hooking up to the top at each support to resist negative moment; distribution/temperature bars run perpendicular, tying the mat together across the long direction.
NSCP 2015 One-Way Slab Thickness Calculator
Select support condition, enter span, fy, and concrete type. Returns minimum thickness, minimum flexural reinforcement As,min, and maximum/practical bar spacing per Section 407.
407.3 — Thickness
NSCP 2015 §407.3.1.1Table 407.3.1.1 — Minimum Thickness of Solid Non-Prestressed One-Way Slabs. Applies to slabs not supporting or attached to partitions or other construction likely to be damaged by large deflections, unless a calculated deflection check per 424.2 shows a thinner slab is adequate.
| Support Condition | Minimum h |
|---|---|
| Simply supported | L / 20 |
| One end continuous | L / 24 |
| Both ends continuous | L / 28 |
| Cantilever | L / 10 |
Expression applicable for normal weight concrete and fy = 420 MPa. For other cases, minimum h shall be modified in accordance with 407.3.1.1.1 through 407.3.1.1.3.
For fy other than 420 MPa, the Table 407.3.1.1 minimum is multiplied by (0.4 + fy/700).
§407.3.1.1.2For non-prestressed slabs made of lightweight concrete with wc in the range 1440–1840 kg/m³, the table value is multiplied by the greater of: (a) 1.65 − 0.0003wc, or (b) 1.09.
§407.3.1.1.3For non-prestressed composite slabs combining lightweight and normal weight concrete, shored during construction, where the lightweight concrete is in compression, the 407.3.1.1.2 modifier applies.
The thickness of a concrete floor finish is permitted to be included in h if placed monolithically with the floor slab, or if the finish is designed to be composite with the slab per Section 416.4.
407.3.2 — Calculated Deflection Limits
407.3.2.1 For non-prestressed slabs not satisfying 407.3.1, and for all prestressed slabs, immediate and time-dependent deflections must be calculated per Section 424.2 and must not exceed the limits in 424.2.2.
407.3.2.2 For non-prestressed composite concrete slabs satisfying 407.3.1, deflections occurring after the member becomes composite need not be calculated. Deflections before compositing must be investigated unless the pre-composite thickness also satisfies 407.3.1.
407.3.3 — Reinforcement Strain Limit (Non-Prestressed)
407.3.3.1 For non-prestressed slabs, the net tensile strain εt shall be at least 0.004.
407.3.4 — Stress Limits in Prestressed Slabs (for completeness)
407.3.4.1 Prestressed slabs are classified as Class U, T, or C per Section 424.5.2. 407.3.4.2 Stresses immediately after transfer and at service loads must not exceed the permissible stresses in Sections 424.5.3 and 424.5.4. Not covered by the calculator on this page — see a licensed engineer for prestressed slab design.
407.4 — Required Strength
407.4.1.1 Required strength is calculated per the factored load combinations in Section 405. 407.4.1.2 Required strength is calculated per the analysis procedures in Section 406. 407.4.1.3 For prestressed slabs, effects of reactions induced by prestressing are considered per 405.3.11.
407.4.2.1 — Factored Moment. For slabs built integrally with supports, Mu at the support is permitted to be calculated at the face of support.
407.4.3.1 — Factored Shear. For slabs built integrally with supports, Vu at the support is permitted to be calculated at the face of support. 407.4.3.2 Sections between the face of support and a critical section located d (non-prestressed) or h/2 (prestressed) from the face may be designed for the Vu at that critical section if: (a) the support reaction, in the direction of applied shear, introduces compression into the end region; (b) loads are applied at or near the top surface; and (c) no concentrated load occurs between the face of support and the critical section.
407.5 — Design Strength
407.5.1.1 For each factored load combination, design strength at every section must satisfy φSn ≥ U, including (a) φMn ≥ Mu and (b) φVn ≥ Vu — interaction between load effects must be considered. 407.5.1.2 φ is determined per Section 421.2.
407.5.2.1 — Moment. Mn is calculated per Section 422.3. 407.5.2.2 For prestressed slabs, external tendons are considered unbonded unless effectively bonded to the section along their entire length. 407.5.2.3 Where slab reinforcement parallel to a T-beam's longitudinal axis forms the flange, perpendicular reinforcement must be provided in the top of the slab to resist the factored load on the overhanging width acting as a cantilever — only the effective overhanging width per 406.3.2 need be considered. Does not apply to joist construction.
407.5.3.1 — Shear. Vn is calculated per Section 422.5. 407.5.3.2 For composite concrete slabs, horizontal shear strength Vnh is calculated per Section 416.4.
407.6 — Reinforcement Limits
§407.6.1 — Minimum Flexural Reinforcement (Non-Prestressed)Table 407.6.1.1 — As,min for Non-Prestressed One-Way Slabs. A minimum area of flexural reinforcement As,min must be provided per this table, regardless of the analysis result — this is a code floor, not a calculated demand.
| Reinforcement Type | fy, MPa | As,min |
|---|---|---|
| Deformed bars | < 420 | 0.0020 Ag |
| Deformed bars or welded wire reinforcement | ≥ 420 | Greater of: 0.0018×420/fy × Ag and 0.0014 Ag |
407.6.2 — Minimum Flexural Reinforcement (Prestressed, for completeness)
407.6.2.1 For slabs with bonded prestressed reinforcement, the total quantity of As and Aps must be adequate to develop a factored load at least 1.2 times the cracking load, calculated on the basis of fr per 419.2.3. 407.6.2.2 Slabs with both flexural and shear design strength at least twice the required strength need not satisfy 407.6.2.1. 407.6.2.3 For slabs with unbonded tendons, minimum bonded deformed longitudinal reinforcement As,min ≥ 0.004Act, where Act is the area of the part of the cross section between the flexural tension face and the centroid of the gross section.
407.6.3 — Minimum Shear Reinforcement
407.6.3.1 Minimum shear reinforcement Av,min is required in all regions where Vu > φVc. For precast prestressed hollow-core slabs with h > 315mm, Av,min is required where Vu > 0.5φVcw. 407.6.3.2 If testing shows the required Mn and Vn can be developed without it, 407.6.3.1 need not be satisfied — tests must simulate differential settlement, creep, shrinkage, and temperature change effects realistically expected in service. 407.6.3.3 Where shear reinforcement is required, Av,min follows Section 409.6.3.3.
Most residential and light-commercial one-way slabs are proportioned so Vu ≤ φVc from concrete alone — shear reinforcement is rarely needed in typical slabs, but must always be checked, never assumed.
407.6.4 — Minimum Shrinkage and Temperature Reinforcement
407.6.4.1 Shrinkage and temperature reinforcement is provided per Section 424.4 (the ratio table itself lives in 424.4, cross-referenced here, not reproduced in Section 407). 407.6.4.2 If prestressed shrinkage/temperature reinforcement per 424.4.4 is used, 407.6.4.2.1–3 apply: for monolithic cast-in-place post-tensioned beam-and-slab construction, gross concrete area is the total beam area plus the slab area within half the clear distance to adjacent beam webs (effective prestress force in beam tendons may be included); if slabs are supported on walls or not cast monolithically with beams, gross area is the slab section tributary to the tendon or tendon group; and at least one tendon is required in the slab between faces of adjacent beams or walls.
407.7 — Reinforcement Detailing
407.7.1 — General
Concrete cover per Section 420.6.1. Development lengths of deformed and prestressed reinforcement per Section 425.4. Splices per Section 425.5. Bundled bars per Section 425.6.
407.7.2.1 Minimum spacing s follows Section 425.2. 407.7.2.2 For non-prestressed and Class C prestressed slabs, spacing of bonded longitudinal reinforcement closest to the tension face must not exceed s calculated per Section 424.3. 407.7.2.3 Maximum spacing s of deformed flexural reinforcement is the lesser of 3h and 450 mm. 407.7.2.4 Spacing required by 407.5.2.3 (T-beam flange transverse reinforcement) must not exceed the lesser of 5h and 450 mm.
Where thickness and spacing meet reality. The formwork elevation fixes h, and the bar mat visible at the slab edge is exactly the spacing the calculator above suggests. Photo: AEDO Construction slab pour in progress.
407.7.3 — Flexural Reinforcement Detailing (Non-Prestressed)
407.7.3.1 Calculated tensile or compressive force in reinforcement at each section must be developed on each side of that section. 407.7.3.2 Critical locations for development are points of maximum stress and points along the span where bent or terminated tension reinforcement is no longer required to resist flexure. 407.7.3.3 Reinforcement must extend beyond the point it is no longer required for flexure by at least the greater of d and 12db, except at simple supports and free ends of cantilevers. 407.7.3.4 Continuing flexural tension reinforcement must have an embedment length at least ℓd beyond the point where bent or terminated tension reinforcement is no longer required.
407.7.3.5 Flexural tension reinforcement must not be terminated in a tension zone unless one of: (a) Vu ≤ (2/3)φVn at the cutoff point; (b) for 36mm bars and smaller, continuing reinforcement provides double the area required for flexure at the cutoff point and Vu ≤ (3/4)φVn; or (c) stirrup area in excess of that required for shear is provided along each terminated bar over a distance 3/4d from the termination point, with excess Av not less than 0.41bws/fyt.
407.7.3.6 Adequate anchorage is required where reinforcement stress is not directly proportional to moment — sloped, stepped, or tapered slabs, or where tension reinforcement is not parallel to the compression face. 407.7.3.7 In slabs with spans not exceeding 3m, welded wire reinforcement (wire size ≤ MW30 or MD30) is permitted to be curved from a point near the top of slab over the support to a point near the bottom at midspan, provided it is continuous over, or developed at, the support.
407.7.3.8 — Termination of Reinforcement (detailed bar-cutoff rules)
407.7.3.8.1 At simple supports, at least one-third of the maximum positive moment reinforcement must extend along the slab bottom into the support (precast slabs: at least to the center of the bearing length). 407.7.3.8.2 At other supports, at least one-fourth of the maximum positive moment reinforcement must extend along the slab bottom into the support at least 150mm.
407.7.3.8.3 At simple supports and points of inflection, db for positive moment tension reinforcement is limited such that ℓd satisfies: (a) ℓd ≤ (1.3Mn/Vu + ℓa) if the end is confined by a compressive reaction, or (b) ℓd ≤ (Mn/Vu + ℓa) if not confined — unless the reinforcement terminates beyond the support centerline with a standard hook or equivalent mechanical anchorage. Mn is calculated assuming all reinforcement at the section is stressed to fy; Vu is calculated at the section. At a support, ℓa is the embedment length beyond the center of the support. At a point of inflection, ℓa is the embedment length beyond that point, limited to the greater of d and 12db.
407.7.3.8.4 At least one-third of the negative moment reinforcement at a support must have an embedment length beyond the point of inflection at least the greatest of d, 12db, and ℓn/16.
407.7.4 — Flexural Reinforcement Detailing (Prestressed, for completeness)
407.7.4.1 External tendons must be attached to the member so as to maintain the specified eccentricity through the full range of anticipated deflections. 407.7.4.2 If non-prestressed reinforcement is required to satisfy flexural strength, it must satisfy the 407.7.3 detailing requirements. 407.7.4.3 Post-tensioned anchorage zones per Section 425.9; anchorages and couplers per Section 425.8. 407.7.4.4 Deformed reinforcement required by 407.6.2.3 in slabs with unbonded tendons must satisfy both: (a) at least ℓn/3 in positive moment areas, centered in those areas; and (b) at least ℓn/6 on each side of the face of support.
407.7.5 — Shear Reinforcement
407.7.5.1 If shear reinforcement is required, transverse reinforcement must be detailed according to Section 409.7.6.2.
407.7.6 — Shrinkage and Temperature Reinforcement Detailing
407.7.6.1 Shrinkage and temperature reinforcement per 407.6.4 is placed perpendicular to the flexural reinforcement. 407.7.6.2.1 — Non-prestressed: spacing of deformed shrinkage and temperature reinforcement must not exceed the lesser of 5h and 450mm.
407.7.6.3 — Prestressed Tendon Spacing (for completeness)
407.7.6.3 Spacing of slab tendons required by 407.6.4.2, and the distance from the face of beam or wall to the nearest slab tendon, must not exceed 1.8m. If tendon spacing exceeds 1.4m, additional deformed shrinkage and temperature reinforcement per 424.4.3 is required parallel to the tendons (424.4.3.4 need not be satisfied). In calculating the additional reinforcement area, gross concrete area is permitted to be the slab area between faces of beams per Table 424.4.3.2. This reinforcement must extend from the slab edge a distance not less than the slab tendon spacing.
Worked Example
Floor slab, one end continuous, span 4.0m, normal weight concrete, fy = 420 MPa, 12mm bars:
| Base thickness h0 = 4000mm / 24 (§407.3.1.1) | 166.7 mm |
| fy modifier (0.4 + 420/700) — fy = 420, so factor | 1.000 |
| Lightweight modifier (normal weight, n/a) | 1.000 |
| Minimum thickness h,min | 166.7 mm |
| Practical thickness (rounded up) | h = 170 mm |
| Ag (1000mm strip) = 1000 × 170 | 170,000 mm² |
| As,min = max(0.0018×420/420×Ag, 0.0014×Ag) = max(306, 238) | 306 mm²/m |
| Max spacing = lesser of (3×170=510) and 450mm (§407.7.2.3) | 450 mm |
| 12mm bar area = 113.1 mm²; spacing to meet As,min = 113.1/306×1000 | ≈369 mm |
| Suggested detailing | 12mm bars @ 350mm o.c. (As provided ≈323 mm²/m) |
This sizing satisfies the deflection-exempt thickness table and the minimum flexural reinforcement — it still must be checked against the actual factored moment Mu and shear Vu for the real loading per Sections 407.4 and 407.5 before being finalized for a permit set.
What This Tool Does Not Replace
This calculator sizes a slab to the deflection-exempt minimum thickness and minimum reinforcement — the starting point of Section 407, not the finish line. A complete one-way slab design still requires:
- Factored moment and shear design (Mu, Vu) against the actual dead, live, and other applicable loads per Sections 405–406, which may govern a thicker slab or more reinforcement than the code minimum
- Full calculated deflection check per Section 424.2 if the slab does not qualify for the exempt table (407.3.2) — e.g. slabs supporting deflection-sensitive partitions
- Shear reinforcement check (407.6.3) if Vu exceeds φVc
- Bar cutoff and development length detailing at every support and inflection point per 407.7.3.8
For a permit-ready structural design, this requires a sealed analysis — which AEDO includes on every structural design project.
Frequently Asked Questions
What is the minimum thickness of a one-way slab per NSCP 2015?
Per Table 407.3.1.1, for normal weight concrete with fy = 420 MPa: simply supported = L/20, one end continuous = L/24, both ends continuous = L/28, cantilever = L/10. These are deflection-exempt minimums — they apply only to slabs not supporting or attached to partitions likely to be damaged by large deflections.
How do you adjust minimum thickness for fy other than 420 MPa?
Multiply the table value by (0.4 + fy/700) per 407.3.1.1.1. At fy = 420 the factor is exactly 1.0; lower-grade steel (e.g. 275 MPa) allows a thinner slab, higher-grade steel (e.g. 500 MPa) requires a thicker one.
What is the minimum flexural reinforcement for a one-way slab?
Per Table 407.6.1.1: 0.0020Ag for deformed bars with fy < 420 MPa; the greater of 0.0018×420/fy×Ag and 0.0014Ag for deformed bars or WWR with fy ≥ 420 MPa.
What is the maximum bar spacing allowed?
For flexural reinforcement, the lesser of 3h and 450mm (407.7.2.3). For shrinkage and temperature reinforcement, the looser limit of the lesser of 5h and 450mm (407.7.6.2.1).
Does minimum thickness alone mean the slab is safe?
No. The Table 407.3.1.1 minimum only satisfies deflection control by exemption — it does not check whether the slab has adequate moment and shear capacity for its actual loading. Both checks (thickness for deflection, and Mn/Vn for strength per 407.4–407.5) must be satisfied; whichever demands more governs the final design.
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| Minimum flexural reinforcement As,min (§407.6.1) | ✓ | ✓ |
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| Full moment/shear design (Mu, Vu, Mn, Vn) | — | ✓ |
| Calculated deflection check (§424.2) | — | ✓ |
| Two-way slab design (§408) | — | ✓ |
| Seismic (§208) & wind (§207A/B) loads | — | ✓ |
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