How to use the construction calculator
It works like a Construction Master or similar jobsite calculator. Numbers you type are an entry. Pressing a function key either stores that entry (if you typed something) or solves it (if you didn't). Results always show in feet, inches and fractions at the precision you pick.
Example 1: add two measurements
9 Ft 7 In 1 ⁄ 2 + 3 Ft 4 In 5 ⁄ 8 = gives 13'-0 1/8".
Example 2: rafter length from run and pitch
Store the run, then the pitch, then ask for the diagonal: 1 2 Ft Run · 6 Pitch · Diag gives 13'-5", the line length of a common rafter on a 12' run at 6/12. Press Rise for the rise (6'-0"), or Hip/V for the hip or valley length (18'-0").
Example 3: stairs
1 0 8 Stair shows 14 risers for a 108" rise. Press Stair again for the riser height (7 11/16"), then the tread, total run and stringer diagonal. It assumes a 7¾" max riser and a 10" tread. While the tread step is showing, type a different tread and press Stair to change it. For a code check and more options, use the stair calculator.
Example 4: jack rafters
With run and pitch stored as in Example 2, type 1 6 O.C., then press Jack. The first press shows the common difference (1'-5 7/8" at 6/12, 16" O.C.). Each press after that shows the next jack, longest first.
Key reference
- Ft / In / ⁄: build a feet-inch-fraction entry. In just closes the whole-inch part before a fraction.
- Pitch, Rise, Run, Diag: the right-triangle keys. Store any two and solve for the others.
- Bd Ft: thickness, width, length (press Bd Ft after each) gives board feet.
- Circ: diameter, then circumference and area in square feet.
- Rake: stud heights under a sloped top plate. Needs a stored Pitch and O.C. Type the shortest stud, press Rake, and keep pressing.
- M+ M− MR MC: memory. CE clears the current entry. AC clears everything.
FAQ
Is this the same as a Construction Master calculator?
It works the same way for everyday framing math: feet-inch-fraction entry, right-triangle keys (pitch, rise, run, diagonal), hip/valley, stairs, jack rafters and board feet. It is free and runs in your phone's browser.
How do I enter feet and inches?
Type the feet, press Ft, type the inches, press In, then the fraction with the ⁄ key. For 9' 7 1/2" press 9 Ft 7 In 1 ⁄ 2. A number without Ft is read as inches.
How do I find rafter length with the calculator?
Enter the run and press Run, enter the pitch (inches of rise per 12) and press Pitch, then press Diag. The result is the common rafter line length. Press Hip/V for the hip or valley.
Can I multiply and divide feet and inches?
Yes. × and ÷ work on lengths in inches. For example, 16 × 12 = 16'-0", or 10' ÷ 3 = 3'-4".