RedX Calc: The 100% Free Construction Calculator App
Free on the App Store and Google Play:
Feet & Inches Calculator: Work the Way You Measure
Full Feet-Inch-Fraction Math
Add, subtract, multiply and divide complete dimensions like 12' 6" + 3' 4" and get answers in the same feet-inch form you read off your tape measure.
Adjustable Fraction Precision
Round results to 1/2", 1/4", 1/8", 1/16" or finer so cut lists match your tape.
Imperial and Metric in One Tap
Dedicated yards, feet, inch, meter, centimeter and millimeter keys convert any entry or result instantly, and the Conv key opens a full unit converter.
Memory Keys and Percent Functions
MC, MR, M+ and M- registers plus percent, square, square root and reciprocal keys cover the math between measurements.
Rafter & Roof Pitch Calculator: Pitch, Rise, Run and Diagonal Keys
Enter What You Know, Solve the Rest
Type a value and press Pitch, Rise, Run or Diag to store it. Press an empty key to solve it. Rafter lengths come back in feet and inches.
Hip, Valley and Jack Rafters
Dedicated Hip/V and Jack keys lay out hip and valley rafters and jack rafter walks, with second functions for irregular dual-pitch roofs.
Miter and Angle Functions
The Miter key and pitch-as-degrees entry handle trim and framing angles without a separate reference chart.
Stairs, Arcs, Circles and Dimensions: One Calculator for the Whole Job
Stair Layouts
The Stair key turns a total rise into risers, treads and stringer numbers, with a riser-limited second function for code-driven layouts.
Arcs, Circles, Columns and Cones
Solve arched openings from chord and height, get full circle facts from any single value, and calculate column and cone volumes.
Length, Width and Height Registers
Store dimensions once and get perimeters, areas and volumes. The math is unit-aware, so results come back in the units you build with.
Step-by-Step Guides Built In
Every function has a guide inside the app covering the basics, roofs, stairs, circles and conversions, so you never have to guess a key sequence.
Automatic Calculation History: Your Tape, Saved
Every Result on the Record
Each completed calculation lands in the History tab with its full expression, so you can check a cut hours later without redoing the math.
Fewer Mistakes on Site
Compare measurements side by side and catch entry errors before they become cutting errors.
Light and Dark Mode: Readable in the Sun, Easy at Night
Big, High-Contrast Display
Large feet and inch readouts with grouped, color-coded keys that stay readable at arm's length.
System, Light or Dark
Follow your phone's theme or lock the calculator to light or dark. The app remembers your choice.
A Construction Calculator for Everyone
Framers & Carpenters
Rafter, stair and miter functions with feet-inch-fraction answers, in the same workflow as a dedicated trade calculator.
Contractors & Builders
Fast dimension math for estimates, takeoffs and on-site changes, with a history you can check back on.
DIYers & Apprentices
The built-in guides teach every function, so you learn feet-inch math and roof geometry while you use the calculator.
Construction Calculator FAQ
Is the RedX Construction Calculator really free?
Yes. RedX Calc is 100% free, forever. There are no ads, no subscriptions and no in-app purchases. Every feature is included, from feet-inch-fraction math to the rafter, stair, arc and circle functions.
How do I add and subtract feet and inches with fractions?
Type a dimension such as 12 Feet 6 Inch + 3 Feet 4 Inch and press equals. RedX Calc keeps everything in feet-inch-fraction form, with adjustable fraction precision, and can convert any result between yards, feet, inches, meters, centimeters and millimeters in one tap.
Can it calculate rafters and roof pitch?
Yes. Use the Pitch, Rise, Run and Diagonal keys: enter the values you know, then tap the key you want to solve. Dedicated Hip/Valley and Jack functions handle hip and valley rafters and jack rafter walks, including irregular (dual-pitch) roofs.
What else can the calculator solve?
Beyond feet and inches math, RedX Calc has function keys for stair risers and treads, arcs and arched openings, circles, columns and cones, compound miters, and length-width-height registers for areas and volumes. Built-in step-by-step guides explain every function.
Does it work in both imperial and metric?
Yes. RedX Calc is unit-aware: mix yards, feet, inches, meters, centimeters and millimeters in the same calculation and convert any result with one tap. Fraction precision is adjustable, so you can round to the increment your tape measure uses.
More RedX Building Tools
Put a Trade Calculator in Your Pocket
RedX Calc gives you feet-inch-fraction math, rafter and stair functions, unit conversions and a full calculation history. 100% free, with no ads and no subscriptions. Download it once and it goes to every jobsite with you.