About the Paint Calculator
Buying too little paint means a second trip and a possible colour mismatch; buying too much wastes money. Enter the room's length, width and wall height, the number of doors and windows, how many coats and the coverage printed on the can. The calculator works out paintable wall area and the paint you need in gallons and litres, rounded up to whole cans.
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The Curator field notes
A closer look at Paint Calculator
FIELD NOTE 1
Most interior paint covers about 350–400 sq ft per gallon per coat.
FIELD NOTE 2
Bare drywall, dark colour changes and textured walls need an extra coat.
FIELD NOTE 3
Buy all cans from the same batch, or mix them in a bucket, to avoid colour shifts.
FIELD NOTE 4
Ceilings aren't included — measure length × width separately for them.
From input to result
- 1
Enter room length, width and wall height in feet.
- 2
Enter doors, windows, coats and coverage.
- 3
Read the gallons and cans to buy.
Category reference · illustrative chart
A month is not a fixed unit of time
In the Gregorian calendar, February has 28 days in a common year and 29 in a leap year. April has 30 and January has 31. These reference examples explain why calendar calculations cannot assume every month lasts 30 days.
February (common) · 28 days
February (leap) · 29 days
April · 30 days
January · 31 days
About everyday tools
Some questions come up again and again: how old is someone exactly, how many days until a deadline, what day of the week was a date. They are easy to get slightly wrong by hand because months have different lengths and leap years move the goalposts.
These helpers use your browser's own calendar maths, which follows the Gregorian calendar used internationally. They are quick, precise and private — handy for forms, planning and settling friendly arguments.
Date arithmetic is a classic source of off-by-one errors. A 'month' can be 28, 29, 30 or 31 days long, a year can be 365 or 366 days, and people born on 29 February have a birthday that only appears every four years. These tools count calendar months first and then the remaining days, which matches how ages are written on official forms. Everything runs on your device, so no dates of birth or personal details are ever stored or transmitted. If you need an age for a legal purpose, check the specific rule used by the organisation asking, as a few jurisdictions count differently.
The unit converters use the exact international definitions agreed in 1959 — one inch is exactly 2.54 centimetres and one pound is exactly 0.45359237 kilograms — so results match engineering references rather than rounded rules of thumb. Health figures such as BMI follow published World Health Organization thresholds and are offered as general information only, never as a diagnosis. Random numbers come from the cryptographic generator built into your browser, the same source used to create secure keys, which makes draws genuinely unpredictable and fair.
Popular ways people use everyday tools
- Confirming an exact age for school enrolment, sports categories, insurance or benefits forms.
- Counting the days left until a birthday, anniversary, deadline or long-awaited trip.
- Working out how old someone was on a particular historical date for family research.
- Settling friendly arguments about who in the family is older and by exactly how many days.
- Converting recipe weights, oven temperatures and luggage limits when travelling between metric and imperial countries.
- Planning milestone celebrations such as a 10,000th day alive or a fortieth birthday.
How we build and test our free tools
Every tool in this collection is built and tested by The Curator team. Before a tool is published we check it against known reference results — textbook loan schedules, standard test vectors for hashes, sample files for conversions — and we re-check it whenever browsers change. Each page explains the method so you can verify the answer yourself rather than take it on trust.
The tools run as JavaScript inside your browser tab. When you choose a file, your browser reads it from your disk into memory; the tool processes it and gives you the result as a download. No copy is sent to us or to anyone else, and nothing is kept after you close the tab. That is why these tools are safe for personal documents, and why they keep working on a slow or interrupted connection once the page has loaded.
The collection is free because it is supported by advertising on these guide pages. We never charge for a tool, never add watermarks and never sell what you type. If something doesn't work as described, or you would like a tool we don't have yet, please contact us — new tools are added in regular batches based on what readers ask for.
Frequently asked questions
- How are doors and windows handled?
- Each door subtracts about 20 sq ft and each window about 15 sq ft.
- Can I use metres?
- Enter sizes in feet; 1 metre ≈ 3.28 feet.
- Is my input stored or sent anywhere?
- No. Everything runs inside your browser tab and disappears when you close it.
- Is the Paint Calculator really free?
- Yes. There is no account, no trial and no watermark. The Curator is supported by advertising on its guide pages, never by charging for tools or selling your data.
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