For iPhone, iPad & Android
The construction calculator that thinks in feet, inches and fractions
Kalku is a jobsite calculator: a real feet-inch-fraction keypad with the keys trades use, and 225 ready-made calculators for every trade, with live 3D previews. Free, with no ads and no account, and it works with no signal.
Not in the stores yet. Meanwhile, try the free calculators that run the same formulas.
Work the way drawings are written
Most calculators make you turn 20' 6-1/2" into 20.5417 before you can do anything with it. Kalku doesn't. Type the dimension as it is written, and the units come along with the numbers: multiply two lengths and you have an area, add a height and you have a volume, divide by an area and you are back to a length. Adding a length to an area is refused, so the units can never quietly go wrong.
Every result is rounded to the fraction you choose, from a half to 1/64 of an inch, and a fraction that rounds up carries into the inches and the feet, so you never read 6-16/16". Prefer metric? Switch the whole app over, or mix units and convert any answer with one key.
What's in Kalku
Feet, inches and fractions
Type 20 Feet 6 Inch 1/2 and the display reads 20' 6-1/2". Fractions from 1/2 to 1/64, reduced or kept in sixteenths, with any answer converted to yards, metres, square or cubic units in one key.
Construction keys
Pitch, rise, run, rafter, hip and valley, jack rafters and rake walls. Stairs, circles, arcs, columns and cones, crown miter and bevel, studs, blocks, drywall and footings. Hold any key for what it does.
225 calculators, 14 trades
From slabs and rebar grids to rafters, wire size, duct size and loan payments. Every figure updates as you type, and each calculator shows its formula underneath.
See what you're building
The slab, the stairs, the roof or the trench is drawn in 3D as you type: drag to turn it, pinch to zoom. Money calculators chart the balance and the breakdown.
Keep it and share it
Save any calculation with a name and a note, and share it as a clean PDF with every input and result, or as text, straight from the job.
Make it yours
Ten visual styles, light or dark, your accent colour, metric mode, decimal comma, your currency and 38 languages.
225 calculators in 14 categories
Fill in a few fields and every figure updates as you type. Search by name or by the trade's own words, star the ones you use, and send any result to the keypad.
Concrete
Slabs, footings, columns and tube forms, walls, curbs, steps, bags, mix ratio, rebar grids, mesh
Foundations
Basement take-off, excavation and backfill, trenches, benching, cut and fill, soil types
Framing
Stud and rake walls, sheathing, joists, subfloor, decks, fences, stairs, balusters, ramps, board feet
Roof
Rafters and cut angles, hips and jacks, pitch, roof area, shingles, metal panels, ventilation, gutters
Floors, walls & ceilings
Drywall, paint, wallpaper, trim, tile and grout, laminate, carpet, drop ceilings, insulation
Masonry
Block, brick, stone veneer, retaining walls, mortar
Paving
Gravel, asphalt, pavers, patio base, mulch and topsoil, parking
Electrical
Ohm's law, watts and amps, breaker size, voltage drop, wire size, box and conduit fill, three-phase
Heating & A/C
BTU estimate, tons, air changes, duct size, heat loss, fuel cost, SEER, EER and COP
Plumbing
Pipe and tank volume, fill time, drain slope, pressure and head, water heaters, pools
Business
Bids, labor cost, markup and margin, break-even, loans, mortgages, leases, depreciation, ROI
Project dates & times
Contract dates, working days, inspection and material dates, crew size for a deadline, timesheets
Shapes & geometry
Areas and volumes of every shape, L, T and U shapes, triangles, squaring a layout
Conversions
Length, area, volume, weight, temperature, pressure, flow, slope, fractions, energy
Try ten of them now, free
The most-used calculators from the app run right here in your browser, with the same formulas, in feet and inches or metric. Nothing to install and nothing to sign up for.
No account. No ads. Your jobs stay on your phone.
Kalku never asks you to sign up, shows no ads and sells nothing. Your settings, calculator forms and saved calculations are stored on your device, and nothing in the app needs a connection. It sends anonymous usage statistics and crash reports to my own analytics server, with no identifier for you or your device and never anything you type, and one switch in Settings turns that off.
Questions
When is Kalku coming out?
Kalku is not in the stores yet. When it is, the buttons on this site will take you straight to the App Store and Google Play. Until then, the free calculators on this site run the same formulas in your browser.
Is Kalku free?
Yes. Kalku has no ads, no subscription and no in-app purchases, and it never asks you to sign up for anything.
Which phones and tablets does it run on?
iPhone and iPad with iOS 15 or later, and Android phones and tablets with Android 7.0 or later. On a tablet the history sits beside the keypad. The app is laid out for portrait.
Does it work without a signal?
Yes, all of it. Every calculator, the 3D previews, your saved calculations and sharing as PDF work with no connection, which is the point on a jobsite. Nothing in the app needs the internet.
Can I use metric?
Yes. Kalku has a metric mode, and in either mode you can enter and convert to millimetres, centimetres, metres, square and cubic metres, kilograms and metric tons as well as feet, inches, yards, acres, board feet, gallons, pounds and tons. Numbers can use a decimal comma and thousands separators, and any currency symbol.
How does feet-inch-fraction entry work?
The way a dimension is written on a drawing. Type 20 Feet 6 Inch 1 / 2 and the display reads 20' 6-1/2". Digits after a unit key belong to the next unit down, so 20 Feet 6 already reads as 20' 6". Answers are rounded to the fraction you choose, from 1/2 to 1/64 of an inch, and shown as 20' 6-1/2", 20'-6 1/2" or 20 ft 6 1/2 in.
More in the FAQ.
Kalku: Construction Calculator
Coming soon to the App Store and Google Play. Free, no ads, no account.
