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 | 'Intact' Tuffaceous Sandstone (UCT ≥ 3 MPa, RQD ≥ 70) | 1,000 kPa |
| 2 | 'Lightly Weathered' Tuffaceous Sandstone (UCT ≥ 1 MPa, RQD ≥ 50) | 500 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 — except Class 5 clay, where no increase is allowed for extra width (Table 304-1 footnote c). A one-third increase is permitted when using the Section 203.4 alternate load combinations that include wind or earthquake. 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. A plan and section drawn to your footing size appear under the result.
Drawn from the footing size, depth and allowable bearing pressure worked out above. The numbered tags are explained in the list under the drawings.
Planning sketch only, not for construction. This tool sizes the footing's bearing area only. Footing thickness, reinforcement, two-way (punching) and one-way shear, column size, dowels and concrete cover are structural design items it doesn't cover, so they're marked "per design" and drawn out of scale.
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 are based on a footing 300mm wide and 300mm deep into natural grade. That is the table's reference size, not the smallest footing NSCP allows: Section 305.1 / Table 305-1 sets minimum footing depth below undisturbed ground of 300, 450 and 600mm, and minimum width of 300, 375 and 450mm, for 1, 2 and 3 floors (tabulated for bearing-wall foundations). Go deeper or wider than 300mm, 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. For Class 5 clay the increase applies to depth only; footnote c allows no increase for width. Separately, a one-third increase is permitted when using the Section 203.4 alternate load combinations that include wind or earthquake. 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. Class 5 clay: depth only, no increase for width.
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 §203.3.1, Pu = the larger of 1.4D and 1.2D + 1.6L): two-way (punching) shear around the column, with the critical section located per NSCP 2015 §413.2.7.2 / §408.4.4.1 and the shear strength per §422.6 — one-way (beam) shear across the footing (§422.5), and flexural design of the rebar mat per NSCP §413.3.3 with §407/§408. 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.
Statutes, codes, official tools and references used or referred to in this article, linked to their source. Links open in a new tab.
Prices, cost bands and rate figures in this article are AEDO Construction's own market and practice figures for Philippine work unless a source is named beside them. Code and statute references above link to the primary text.
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.
An engineer designs the isolated footings of a 2-storey house in STAAD Foundation. From the AEDO YouTube channel, uploaded 2021-02-07.
NSCP 2015 Section 304 / Table 304-1 gives a presumptive allowable foundation pressure by soil classification (50-1,000 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 basis. The footing is then checked under factored loads for two-way (punching) shear (critical section per NSCP §413.2.7.2 / §408.4.4.1, strength per §422.6), one-way shear, and flexure (NSCP §413.3.3 with §407/§408) 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: 'intact' tuffaceous sandstone — UCT ≥ 3 MPa, RQD ≥ 70 (1,000 kPa), 'lightly weathered' tuffaceous sandstone — UCT ≥ 1 MPa, RQD ≥ 50 (500 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 — except Class 5 clay, which gets no increase for width. A one-third increase is permitted with the Section 203.4 alternate load combinations that include wind or earthquake. The 300mm basis is not the minimum footing: Table 305-1 sets minimum depth at 300 / 450 / 600mm for 1 / 2 / 3 floors.
