Gallons, yards, and BTUs, before you are standing in the aisle.
The home tools on this site are measuring tools. They do not know your house. They do know the arithmetic that turns a tape measure into a purchase, which is the part people get wrong in the parking lot.
The paint calculator uses wall area of 2 × (length + width) × height, then subtracts about 20 square feet for a door and 15 for a window. A 12 by 10 foot room with 9 foot walls, one door, and two windows has 346 square feet to paint. Two coats at 400 square feet per gallon is 1.73 gallons. The 10% buffer makes 1.90, and you buy 2 gallons because paint is sold that way.
The ceiling is separate. It is 120 square feet, another 0.60 gallons at two coats, and with the buffer the walls-plus-ceiling job crosses into a third gallon. If you are painting the ceiling, add it. The coverage presets, 350, 400, and 450, are a range. The number on the can wins. If the house was built before 1978, disturbing old paint is an EPA lead-paint question, not just a gallon question.
The concrete calculator turns a slab into cubic yards (cubic feet divided by 27) and into bags. A 10 by 12 foot patio, 4 inches thick, is 40 cubic feet. Ten percent extra is 44 cubic feet, 1.63 cubic yards. An 80 pound bag yields about 0.60 cubic feet on QUIKRETE’s concrete-mix sheet, so the bag count is about 74. That is a lot of bags. Around a yard, a truck starts to make sense, and you still need a compacted base and a plan for a short-load fee. Their own calculator notes that yields ignore waste and an uneven base. Order a little over, not the exact yard.
A 20 by 8 foot bed at 3 inches, plus 5%, is 42 cubic feet on the mulch calculator, about 1.56 yards, or 21 of the 2-cubic-foot bags. One bulk yard covers most of it. The ton figure uses about 800 pounds per yard for mulch. Wet mulch weighs more. Ask the yard if you are buying by the ton. Do not use the mulch weight for gravel. The page uses about 2,800 pounds per yard for that.
Flooring is boxes, not square feet. On the flooring calculator, a 12 by 14 room plus a 10 by 10 room is 268 square feet. Ten percent for cuts makes 295. At 20 square feet a box you buy 15 boxes, 300 square feet, about $1,050 at $3.50 a square foot. Stepping the waste up to 15% is one more box. Keep the leftover for the next dent. Underlayment and labor are not in that price.
The BTU calculator starts at 20 BTU per square foot, then adds 600 BTU for each person past two and stretches for a tall ceiling. A 300 square foot room with two people comes out at 6,000 BTU. Energy Star’s room-unit chart puts 250 to 300 square feet at 7,000 BTU and 300 to 350 at 8,000, and then says to add 10% for a sunny room, subtract 10% for deep shade, add 600 BTU per extra person, and add about 4,000 if the unit is in a kitchen. This page is a little low of that chart before those adjustments. A unit that is too big cools the air and shuts off before it dries the room. Match the chart, then buy the size you measured, not the size that was on sale.
If the project is a kitchen you hope to get back at resale, the renovation page multiplies cost by a rounded recoup percent. A $25,000 mid-range kitchen at the menu’s 74% is $18,500 back and a $6,500 gap. That percent is not this year’s local study. Price the paint and the floor before you believe one contractor number.
Last updated: October 29, 2026. Estimates only. Not tax, legal, financial, or professional advice. See the terms.