Whether you hang doors, lay tile, run cable, fix cars or weld frames, most of your math is the same few steps: measure, allow for waste, convert units, and price labor and materials with a margin. This calculator for contractors and tradespeople keeps each step on its own line, so the client can see where the number came from and you can change one measurement without starting over.
Each example below shows what Notes Calculator answers for every line. Choose Open in Notes Calculator under any of them to open it as a note in the web app and swap in your own measurements.
From floor area to a tile order
Tilers and flooring installers start with the room. Multiply feet by feet and you get square feet, so two rooms add up to one floor area. Divide by the area of one tile, add a cut allowance, and round the boxes up.
| Note | Result |
|---|---|
| bathroom = 8 ft x 6 ft | 48 ft² |
| hallway = 10 ft x 4 ft | 40 ft² |
| floor area = bathroom + hallway | 88 ft² |
| tile = 12 in x 12 in | 144 in² |
| tiles = floor area / tile | 88 |
| order = tiles + 10% | 96.80 |
| Boxes of 10 tiles: order / 10 rounded up | 10 |
The allowance is a judgment call: diagonal layouts and small rooms with many cuts usually need more than 10%. Change the percentage on the order line and the box count follows. For more on measuring irregular rooms, lots and fields, see the area calculator guide.
Paint for two coats
Painters work from wall area rather than floor area. The perimeter of the room times the wall height gives the walls; take off doors and windows, multiply by the number of coats, and divide by what one gallon covers. The coverage figure is on the can, usually between 250 and 400 square feet per gallon.
| Note | Result |
|---|---|
| walls = 2 * (14 ft + 12 ft) * 8 ft | 416 ft² |
| openings = 40 ft² | 40 ft² |
| coats = 2 | 2 |
| coverage = 350 ft² | 350 ft² |
| Gallons: (walls - openings) * coats / coverage | 2.15 |
Metric stock from an inch drawing
Fabricators, welders and carpenters often get a drawing in inches and a supplier price list in millimeters or meters. Convert the sizes you need to order, then work out how much stock the cut list uses and how many bars or boards that is.
| Note | Result |
|---|---|
| // drawing in inches, supplier sells metric stock | |
| Plate thickness: 0.25 in to mm | 6.35 mm |
| Flat bar width: 1.5 in to mm | 38.10 mm |
| cut length = 48 in to mm | 1,219.20 mm |
| cuts = 6 | 6 |
| stock = cut length * cuts | 7,315.20 mm |
| stock to m | 7.32 m |
| Bars of 6 m: stock / 6 m rounded up | 2 |
Add a kerf or offcut allowance the same way as the tile allowance, with stock + 10%, if your saw or layout needs it.
Voltage drop on a cable run
Electricians can check a run before choosing the cable. The current comes from the load and the supply voltage; the drop is twice the run length (out and back) times the current times the cable’s resistance per meter (in milliohms here), which you take from the manufacturer’s table.
| Note | Result |
|---|---|
| voltage = 240 | 240 |
| load = 3600 | 3,600 |
| current = load / voltage | 15 |
| run = 30 | 30 |
| milliohms per meter = 6.8 | 6.80 |
| drop = 2 * run * current * milliohms per meter / 1000 | 6.12 |
| drop / voltage as % | 2.55% |
A job quote with labor, parts and markup
Plumbers, mechanics and welders price a job the same way: labor hours at your rate, parts and consumables (filler wire, shielding gas, fittings, fluids) with a markup, then a deposit before you order.
| Note | Result |
|---|---|
| labor hours = 6 | 6 |
| hourly rate = 75 USD | $75 |
| labor = labor hours * hourly rate | $450 |
| parts = 480 USD | $480 |
| consumables = 55 USD | $55 |
| materials = (parts + consumables) + 20% | $642 |
| quote = labor + materials | $1,092 |
| Deposit: 30% of quote | $327.60 |
Price a change order by copying the same lines below a blank line and changing the hours and parts. If you quote training sessions or workshops as well as site work, the workshop quote template adds a minimum price to the same labor plus materials structure, and the profit margin guide explains the difference between a 20% markup and a 20% margin.
Quick conversions on site
Not everything needs a full note. Mechanics can type 35 psi to bar while reading a European spec sheet, plumbers 22 mm to in for a pipe size, and anyone can type 2 gallons to liters for a fluid volume. The unit converter guide lists the length, area, volume and temperature units you can use.
When you are ready, start in the browser at app.notescalculator.com, or see what Lifetime adds if you want one note per job synced to your phone.