Foundation Calculator Footings. Foundation footing calculations require perimeter and dimensions. Formula: Cubic Yards equals (Length times Width times Depth in feet) divided by 27. Example 120-foot perimeter, 24-inch wide, 12-inch deep footing: 120 times 2 times 1 equals 240 cubic feet divided by 27 equals 8.89 cubic yards, order 9 yards concrete. Footing width and depth: Load-bearing requires engineering but rules of thumb exist. Single-story house 16-inch wide by 8-inch deep minimum. Two-story 20-24 inch wide by 10-12 inch deep. Heavy masonry requires wider 24-30 inches. Depth below frost line critical, varies by region 24-48 inches. Local building codes specify exact requirements based on soil and climate. Frost heave pushes footings up if too shallow causing cracking. Rebar reinforcement: Continuous horizontal rebar 2 bars minimum running full length. 1/2-inch diameter (#4 rebar) standard residential. Lapped splices 30-40 diameters (15-20 inches for #4). Vertical rebar from footing into wall every 4 feet ties foundation together. Rebar positioned 3 inches from bottom, 3 inches from edges minimum concrete cover prevents corrosion. Costs: Concrete ready-mix 100-150 per cubic yard. Rebar 0.50-1.00 per linear foot. Formwork 2-4 per linear foot. Labor excavation, forming, pouring 15-30 per linear foot. Example 100 linear feet footing 20×10 inches: concrete 600, rebar 100, forms 300, labor 2,000, total 3,000 or 30 per foot. Foundation types: Strip footing continuous under bearing walls, most common. Spread footing isolated pads under columns. Mat slab entire floor area thickened edge, clay soils. Pier and beam concrete piers with grade beams, expansive soils. Each has specific calculation methods and applications. Excavation depth: Dig below frost line plus footing thickness. Example 36-inch frost line plus 12-inch footing equals 48 inches deep trench. Width includes footing plus working room 6-12 inches each side for formwork access. Sloped sides in sandy soils prevent cave-ins. Shoring required for deep trenches per OSHA over 5 feet. Soil bearing capacity: Determines footing width. Typical soil 1,500-2,500 PSF (pounds per square foot) bearing capacity. Poor soil requires wider footings or engineered solutions like helical piles or soil stabilization. Soil test recommended for large structures provides bearing capacity and frost depth. Costs 500-1,500 for basic residential soil test. Footing forms: Wood 2×10 or 2×12 boards for sides. Stakes every 3-4 feet. Snap chalk line for straight. Level top of forms carefully ensures level foundation walls. Commercial footing forms reusable steel or aluminum. Large projects use continuous forms, small projects trench method pours directly in excavation sides as forms. Common mistakes: Not digging below frost line, heaving and cracking inevitable in freeze-thaw climates. Footing not level, foundation walls built on slope causes structural issues. Insufficient width for load, settling and cracking. Forgetting rebar, unreinforced concrete cracks under stress. Pouring in rain or freezing weather, weakens concrete. Not inspecting before pouring, inspection required before concrete covers everything. Pro tips: Dig trenches slightly wider and deeper than minimum allows adjustment and working room. String lines level marks around entire perimeter ensures consistent depth. Pour concrete in sections if large area, prevents cold joints plan strategically. Vibrate concrete removes air pockets, stronger denser concrete. Screed top level provides flat surface for foundation wall. Cover with plastic for 7-day moist cure. Set anchor bolts while concrete fresh for sill plate attachment, 4-6 feet spacing. Stepped footings: Sloped sites require stepping footings maintains level sections. Steps overlap minimum 2 feet or one footing depth. Rebar continuous through steps with bends. Maximum step height equal to footing depth usually. Engineer steps for steep slopes or high walls. Each step requires separate forming and careful coordination. Foundation drainage: Perimeter drain tile prevents water buildup against foundation walls. 4-inch perforated pipe in gravel at footing level. Slopes to daylight or sump pit. Backfill with gravel around pipe before covering with soil. Damp-proof or waterproof foundation walls prevents moisture problems. Drains can double project cost but essential for dry basements. Building codes and permits: Foundation permit required most areas 200-500. Engineered plans for two-story or poor soils adds 1,000-3,000 engineering fee. Inspections at excavation, rebar placement before pour, final. Setbacks from property line typically 5-10 feet check zoning. Easements may restrict building locations utilities or drainage. Footer vs footing: Footer is person who walks. Footing is concrete base for foundation. Spell correctly on permits and plans or confused contractors. Foundation vs footing: Footing spreads load at base. Foundation wall vertical structure on footing supporting building. Both together form foundation system. Footing always under foundation wall at bottom transferring load to soil. FAQ: How deep should footings be? Below frost line 24-48 inches depending on region plus footing thickness 8-12 inches. How wide? Single-story 16 inches minimum, two-story 20-24 inches, depends on load and soil. How much concrete? Calculate length times width times depth in feet, divide by 27 for cubic yards. Do I need rebar? Yes always, two horizontal bars minimum plus vertical every 4 feet. Can I DIY footings? Possible for small projects like sheds. House foundations hire professional concrete contractor, critical structural element. When is inspection? Before pouring concrete, inspector checks depth, width, rebar placement, must pass before pour.