How to enter a dimension
A dimension on a drawing reads 7’-6 7/8". The calculator takes it as three things, because that is what it is: 7 in the feet box, 6 in the inches box, and 7/8 picked from the fraction menu. There is nothing to parse, so there is nothing to misread. Written as text, 7’-6-7/8" could be a dimension or a subtraction; typed into boxes, it can only be one thing.
The boxes are forgiving where the notation is. Inches over 12 carry: 0 ft 30 in is 2’-6". A box left empty is zero. A negative result reads with one sign for the whole value, −1’-3", never as feet and inches of opposite sign.
In decimal feet and in millimetres there is one box per value, and a decimal is a decimal: 7.5729 ft, or 2308 mm.
| Typed | Feet and inches | Decimal feet | Inches | Millimetres |
|---|---|---|---|---|
| 7 ft, 6 in, 7/8 | 7’-6 7/8" | 7.5729’ | 90.875" | 2308 mm |
| 12 ft, 0 in | 12’-0" | 12’ | 144" | 3658 mm |
| 3 ft, 11 in, 1/4 | 3’-11 1/4" | 3.9375’ | 47.25" | 1200 mm |
| 0 ft, 30 in | 2’-6" | 2.5’ | 30" | 762 mm |
Fractions are a menu, and what the ≈ means
Set the precision once: round to 1/8, 1/16, 1/32 or 1/64 of an inch. The fraction menu then offers only the fractions on that grid, reduced, so 8/16 appears as 1/2 and you cannot type a 3/5. The setting is remembered in your browser between visits; most offices work at 1/16 and never touch it.
The arithmetic is carried exactly and rounded only for display. When a result does not land on the grid you chose, the first line carries a ≈: 10’-0" divided by seven at 1/16 reads ≈1’-5 1/8", because 17.1429 inches does not sit on a sixteenth. The exact value is still underneath, in decimal feet and inches, and it is the exact value that carries forward when you chain.
Rounding carries the way a dimension string carries. 11 63/64" rounded to 1/16 is 1’-0", not 0’-12".
Add, subtract, multiply, divide
Plus and minus take two dimensions. Multiply and divide take a dimension and a plain number: a stair run of 11" times 14 risers, a 12’-0" bay split into three. The calculator will not multiply a dimension by a dimension, deliberately. That is an area, and an area calculator that hides inside a length calculator is how a square-foot number ends up on a drawing with the wrong units.
Dividing by zero shows a dash rather than an error, and the boxes keep their values so you can fix the one that was wrong.
Three systems, every conversion
Pick feet and inches, decimal feet or metric at the top, and the boxes for that system appear. Whatever you work in, the result reads in the others: feet and inches to decimal feet for a survey, decimal feet back to feet and inches for the drawing, millimetres for a European product sheet. There is no separate convert mode; a single value in the first box with nothing to add to it converts on its own.
The conversions are the exact ones: 12 inches to the foot, 25.4 millimetres to the inch, no rounding until the display. Millimetre results in the metric system show tenths; in the other systems they show whole millimetres, which is what a product sheet gives you.
Grade: rise over run
In decimal feet, switch Grade on and the boxes become two elevations and a run. The calculator takes elevation A minus elevation B as the rise and gives the grade two ways: as a percentage, and as a ratio of one vertical to so many horizontal, 1:19. Both are the forms a site plan and a code book use.
A rise of 1.00’ over a run of 12.00’ reads 8.33% and 1:12. A 3.00’ fall across a 60.00’ parking bay reads 5% and 1:20. Leave the run empty and you get the rise alone, which is often the question.
Chaining and copying
Use as first value carries the result into the first box and clears the second, so a running total is a sequence of entries rather than a sequence of retypings. Because the value carried is the exact one, not the rounded display, a chain of twenty additions at 1/16 is still correct to the sixty-fourth. Copy puts the first line on the clipboard without the ≈, ready for a dimension string or an email.
Where it came from
This is the calculator that rides beside DOC, LODE’s AI assistant, inside the app: open the drawer from anywhere, do the arithmetic, close it. It never sends a message or spends a DOC question, which is why it is free on every plan, and why it is free here. The same code runs on this page. Nothing you type leaves your browser; the only thing stored is which system and which precision you last used.
Frequently asked questions
How do I add feet and inches?
Type the first dimension as feet, inches and a fraction from the menu, choose +, type the second the same way. The result reads in feet and inches, decimal feet, inches and millimetres at once. Inches over 12 carry, so 7’-9" plus 0’-5" is 8’-2".
How do I convert feet and inches to decimal feet?
Enter the dimension in the first boxes and leave the second empty. The decimal-feet line is the conversion: 7’-6 7/8" is 7.5729’. It works the other way from the decimal feet system, and to millimetres from either.
How do you calculate the grade or slope as a percentage?
Rise divided by run, times 100. In the decimal feet system turn Grade on, enter the two elevations and the run between them, and the calculator gives the percentage and the 1:n ratio together: a 1’ rise over 12’ is 8.33% and 1:12.
What does the ≈ in front of a result mean?
That the exact answer does not land on the fraction grid you chose, so the feet-and-inches line is rounded to it. The decimal lines underneath are exact, and the exact value is what carries forward if you chain.
Does it calculate square footage?
No. It multiplies a dimension by a number, not by another dimension, because the result of that is an area and this is a length calculator. Keep areas in a tool that says square feet on the answer.
Is anything uploaded or saved?
No. The arithmetic runs in your browser and nothing is sent anywhere. The browser remembers which unit system and precision you last used, and nothing else.