How do I size a footing?

Divide the load the footing carries by your soil's allowable bearing pressure to get the required bearing area. For a square footing, the side length is the square root of that area; for a round pier, the diameter is √(4·Area/π); for a continuous wall footing, the width is the load per linear foot divided by the soil pressure.

What soil bearing value should I use?

Without a soil test, IRC Table R401.4.1 gives conservative presumptive values: 1,500 psf for soft clay, 2,000 psf for typical clay/sand/silt, 3,000 psf for sandy gravel, and 4,000+ psf for rock. A geotechnical report can justify higher values.

Does this size the rebar and thickness too?

No — it sizes the bearing footprint only. Footing thickness, rebar, and punching-shear checks for heavily loaded pads need a designer or the prescriptive IRC footing tables. Use this to get the plan dimensions, then detail the reinforcement per code.

Footing Size Calculator

Size concrete footings from the load they carry and your soil's bearing capacity. Square pad footings, round (pier) footings, and continuous wall footings — using IRC presumptive soil bearing values.

Soil bearing is everything. These are IRC presumptive values — conservative defaults when no soil test exists. A geotechnical report can allow higher (or require lower) values. This sizes for bearing only; thickness, rebar, and punching shear for heavily-loaded pads still need a designer.

Footing type

Soil type

Total load on footing (lb)

Column/post load including tributary roof + floor + dead load.

Required square footing side

37.9

in (exact)

Build to (rounded up)

Required bearing area

10.00

sq ft

At 2,000 psf allowable bearing, a 38" square footing keeps soil pressure within code for a 20,000 lb load.

Did this help?

How to Use This Calculator

Pick the footing type, choose your soil type (or enter a known allowable bearing pressure from your geotech report), and enter the load. For square and round footings, enter the total column/post load in pounds. For a continuous wall footing, enter the load per linear foot. The calculator returns the minimum footing size so soil pressure stays within the allowable.

Formula Used

Required bearing area = Load / Allowable soil pressure. Square side = √Area. Round diameter = √(4·Area/π). Continuous footing width = Load-per-foot / Allowable soil pressure. Soil values from IRC Table R401.4.1 presumptive load-bearing values.

Wood Beam & Joist Designer (NDS)Wall Framing Calculator Stair Calculator

Best GC Software →

Juggling estimates, schedules, and invoices across multiple projects? Contractor software keeps everything in one place — quotes, change orders, sub schedules, and payments.

Compare Carpentry Software Options Not sure which software fits your business? Take the quiz

Need to figure out what to charge?

All 10 pricing formulas + 18-trade gross margin benchmarks.

Contractor Pricing Formulas Cheatsheet→

Starting or growing your carpentry business?

Our free startup guide covers licensing, LLC formation, insurance, pricing, and getting your first customers.

How to Start a Contracting Business→

Free Software Guide for Carpentry Professionals

Get our free guide comparing the best software tools for carpentry businesses — with real pricing and honest recommendations.

No spam. Unsubscribe anytime.

Disclaimer

This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.

How to Use This Calculator

Formula Used

Related Carpentry Calculators

Need to figure out what to charge?

Starting or growing your carpentry business?

Free Software Guide for Carpentry Professionals