Area & Design Calculators
Calculate square footage, stair dimensions, construction areas, and AC unit sizing for residential and commercial building projects.
Square Footage Calculator
Calculate the square footage of rooms and spaces for flooring, painting, and renovation projects.
Stair Calculator
Calculate stair dimensions including rise, run, number of steps, and stringer length.
Construction Area Calculator
Calculate the built-up area, carpet area, and super built-up area for construction projects.
AC BTU Calculator
Calculate the right air conditioner BTU size for your room based on area and conditions.
How to Choose the Right Area Calculator
The Square Footage Calculator handles multi-room layouts, giving you total area across all spaces with automatic metric and acre conversions. This is essential for real estate listings, flooring estimates, and HVAC sizing.
For staircase design, the Stair Calculator ensures your dimensions meet the International Residential Code. It calculates the number of risers, tread depth, total run, and stringer length while flagging any code violations.
The Construction Area Calculator handles basic geometric shapes for lot calculations, foundation planning, and landscaping layouts. For AC unit sizing, the AC BTU Calculator provides room-specific recommendations with adjustments for sun exposure, insulation quality, occupancy, and kitchen placement.
Understanding Area Measurement and Building Design
Accurate area measurement is the foundation of every construction project. Whether you are planning a renovation, buying materials, or sizing HVAC equipment, getting the square footage right prevents expensive mistakes.
For real estate purposes, the American National Standards Institute (ANSI) Z765-2021 standard defines how residential square footage should be measured. Only finished, heated living space above grade counts toward the total. Garages, unfinished basements, and covered porches are measured separately.
The International Residential Code (IRC) sets specific requirements for staircase dimensions. Maximum riser height is 7-3/4 inches, minimum tread depth is 10 inches, and minimum stair width is 36 inches. The code also requires consistent riser heights throughout — variation of more than 3/8 inch between the tallest and shortest riser is a violation.
AC sizing requires more than just square footage. A unit that is too small will run constantly and fail to cool the space, while an oversized unit short-cycles (turns on and off frequently), wasting energy and failing to properly dehumidify. Professional HVAC contractors use Manual J calculations, but our calculator provides a reliable estimate for planning purposes.
Frequently Asked Questions
How do I measure square footage of a room?
Measure the length and width of the room in feet and multiply them together. For irregular shapes, divide the room into rectangles, calculate each area separately, and add them together. Include closets if they are accessible living space.
What is the code for stair riser height?
The IRC sets a maximum riser height of 7-3/4 inches (196.85mm) and a minimum tread depth of 10 inches (254mm). All risers must be consistent within 3/8 inch of each other. Local codes may be stricter, so check with your building department.
What is the difference between BTU and AC BTU calculators?
The BTU Calculator estimates heating AND cooling loads for an entire building, while the AC BTU Calculator specifically sizes air conditioning units for individual rooms with more granular adjustments for sun exposure, kitchen heat, insulation quality, and occupancy levels.
How accurate are online square footage calculators?
Online calculators are highly accurate for rectangular and simple shapes. For complex floor plans, measure each section separately and sum the areas. For legal purposes like real estate listings, an ANSI-compliant professional measurement is recommended.
Can I build stairs without meeting code?
Stairs in livable spaces must meet local building codes (usually based on IRC). Non-code-compliant stairs may not pass inspection, can affect home insurance, and may create liability issues. For non-regulated structures like outdoor garden stairs, code compliance is recommended but may not be legally required.