Sizing footings from a guess instead of a bearing capacity? Get it engineered properly.
Most residential footings in the Philippines are still sized by habit — "the mason always does 600×600" — rather than by the load the column actually carries and what the soil underneath can hold. NSCP 2015 answers both halves of that question directly: Section 304 and Table 304-1 set a presumptive allowable bearing pressure by soil classification, which is exactly what you need to size a footing before a soil report exists. Here's how it works, plus a calculator that runs the numbers for you.
A footing's job is to spread a column's point load over enough soil area that the pressure on the ground stays under what that soil can safely carry. The governing relationship is simple: required footing area = design load ÷ allowable bearing pressure. The load comes from your structural analysis (or a reasonable estimate for preliminary sizing); the allowable bearing pressure comes either from an actual soil investigation, or — when none exists yet — from NSCP 2015 Table 304-1, the Code's presumptive bearing-pressure table by soil classification.
NSCP 2015 Table 304-1 (Allowable Foundation and Lateral Pressure) sets a presumptive value for 5 soil/rock classifications — used when no site-specific soil investigation has established a tested bearing capacity:
| Class | Material | Allowable Foundation Pressure |
|---|---|---|
| 1 | Massive Crystalline Bedrock | 200 kPa |
| 2 | Sedimentary & Foliated Rock (bedded limestone, sandstone, siltstone, shale) | 100 kPa |
| 3 | Sandy Gravel and/or Gravel (GW, GP) | 100 kPa |
| 4 | Sand, Silty Sand, Clayey Sand, Silty Gravel, Clayey Gravel (SW, SP, SM, SC, GM, GC) | 75 kPa |
| 5 | Clay, Sandy Clay, Silty Clay, Clayey Silt (CL, ML, MH, CH) | 50 kPa |
Base assumption: these values apply to footings with a minimum 300mm width and 300mm depth into natural grade. An increase of 20% is allowed for each additional 300mm of width and/or depth, up to a maximum of 3 times the table value — see the depth bonus section below.
Table 304-1 is conservative by design — a real soil boring test (SPT) almost always gives you a higher, site-specific bearing capacity, which means smaller, cheaper footings than the presumptive table alone.
Request a QuoteEnter the column's dead and live load, an optional base moment, the soil class, and footing depth. Get a preliminary square-footing size per NSCP Table 304-1, plus the ultimate (factored) load and an eccentricity check.
The same column load needs a very different footing size depending on which of the 5 classes your soil falls into — swipe through to see how bearing pressure and relative footing size scale across the range.
Table 304-1's base values assume the minimum footing NSCP allows: 300mm wide, 300mm deep into natural grade. Go deeper or wider, and the Code rewards it — a 20% increase in allowable bearing pressure for each additional 300mm of width and/or depth, capped at 3 times the table's base value. This is why the calculator above asks for footing depth: a footing set 900mm below grade (two 300mm increments beyond the 300mm base) on Class 4 soil gets a 40% bearing-pressure bonus — 105 kPa instead of 75 kPa — before any soil test even happens.
The table value applies exactly as printed — no bonus, no penalty.
One additional 300mm increment of width or depth beyond the base earns a 20% increase in qa.
Each further 300mm increment adds another 20%, compounding additively (not multiplicatively) — always checked against the 3× ceiling.
No matter how deep or wide, the bonus stops accumulating once bearing pressure reaches 3 times the base Table 304-1 value for that soil class.
Everything above sizes the footing's plan area using service (unfactored) loads against allowable soil pressure — how wide and long it needs to be so the soil pressure stays within limits. It does not size the footing's thickness or its reinforcement, which come from a separate structural check under factored loads (NSCP 2015 §203, Pu = 1.2D + 1.6L): two-way (punching) shear around the column per NSCP 2015 §413 (Foundations) with §422.6 — the critical section at d/2 from the column face, identical to ACI 318's §22.6 — one-way (beam) shear across the footing, and flexural bending per NSCP §409/§413 that sets the rebar mat. NSCP 2015's structural concrete provisions (Section 4) closely mirror ACI 318-14's chapter structure and numbering, so ACI 318 design references and software remain directly applicable. A footing sized correctly for bearing pressure but under-designed for punching shear can still fail — bearing capacity and structural adequacy are two different checks that both have to pass.
Table 304-1 is meant as a starting point or for small, light structures on evidently competent soil — not a permanent substitute for an SPT boring test on anything beyond that.
The calculator above includes a service-load eccentricity/kern check (qmax/qmin against the adjusted allowable pressure) once you enter a base moment. What it doesn't do is resize the footing automatically when eccentricity governs, or design for biaxial moment (moment about both axes at once) — a corner column with significant two-way moment still needs an engineer's iteration.
Closely spaced footings can overlap their zones of influence in the soil, effectively reducing the bearing capacity each one can rely on individually — a check independent sizing tools like this one don't perform.
From a soil investigation through footing plan area, thickness, and reinforcement, AEDO's engineers design foundations against NSCP 2015 — not a generic template or a mason's habit.
AEDO Construction provides full structural design services (footings, columns, beams, slabs) anywhere in the Philippines, plus full design-build execution in Negros Oriental. One licensed engineer, start to finish.
A footing that's "always 600×600" is either wasting concrete on light columns or under-sized for heavy ones — the load and the soil classification are what actually decide the number. Table 304-1 gets you a defensible preliminary size before a soil report even exists.
NSCP 2015 Section 304 / Table 304-1 gives a presumptive allowable foundation pressure by soil classification (50-200 kPa). Required footing area equals the column's service (unfactored) load divided by the allowable bearing pressure for that soil class, adjusted for footing width and depth beyond the table's 300mm minimum. The footing is then checked under factored loads for punching shear (NSCP §413 with §422.6, matching ACI 318 §22.6), beam shear, and flexure (NSCP §409/§413) to set thickness and reinforcement.
Table 304-1 (Allowable Foundation and Lateral Pressure) is NSCP 2015's presumptive bearing-pressure table, used when no soil investigation has established a site-specific value. It lists 5 classes: massive crystalline bedrock (200 kPa), sedimentary/foliated rock (100 kPa), sandy gravel/gravel — GW, GP (100 kPa), sand/silty/clayey sand and gravel — SW, SP, SM, SC, GM, GC (75 kPa), and clay/sandy clay/silty clay/clayey silt — CL, ML, MH, CH (50 kPa).
For preliminary sizing and small, light structures on evidently competent soil, yes. For most other projects — and anything permit-bound — a licensed engineer will call for an actual soil boring/SPT test, since presumptive values are conservative generic classifications, not a substitute for the site's real, tested bearing capacity.
Table 304-1's values apply to footings with a minimum 300mm width and 300mm depth into natural grade. Each additional 300mm of width and/or depth adds 20% to the allowable pressure, up to a maximum of 3 times the base value.