Free home project calculators

Home project calculators that show the math.

Work out how much paint, concrete, flooring, tile, drywall, mulch, fencing, decking, or roofing to buy before you start the job. Every estimate includes waste, cost, a shopping list, and the formula.

No accountShows the formulaBuilt for store runs
A table with measuring tools, tile samples, a notepad, and a phone calculator for planning a home project.
Calculator-first pagesInstant result, shopping list, formula, and shareable URL.
Project calculator

Paint Calculator

Estimate gallons of paint and primer for a room, including doors, windows, coats, and a practical waste buffer.

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Open full page
Estimate$126

3 gallons

734.8 sq ft of paint coverage after waste

Shopping list

  • 3 gallons of finish paint
  • 1 primer gallon if covering bare drywall or stains
  • Roller covers, tray liners, brush, tape, and drop cloths

Show the math

  1. Wall area = 2 x (12 + 12) x 8 - openings = 334 sq ft
  2. Coverage needed = 334 x 2 coats x 1.1 waste = 734.8 sq ft
  3. Gallons = 734.8 / 350, rounded up = 3
Measure unusual rooms wall by wall.Dark colors and textured walls may need lower coverage.

Calculator library

DIY material calculators for every small project.

Each tool includes waste, rounded buying quantities, cost estimates, and visible math. See all calculators.

Paint CalculatorBest for a quick store run before painting one room or several similar rooms.Mulch, Soil, and Gravel CalculatorBest for landscaping beds, gravel paths, raised areas, and topsoil orders.Flooring Box CalculatorBest before buying boxed flooring at a home center or local flooring shop.Tile CalculatorBest for planning a bathroom floor, laundry room, backsplash, or entryway tile job.Drywall Sheet CalculatorBest for finishing a room, garage wall, closet, or patch-heavy remodel.Concrete Bag vs Ready-Mix CalculatorBest for slabs, pads, footings, and post holes where depth matters.Fence Material CalculatorBest for early planning before requesting quotes or shopping for a simple fence line.Deck Material CalculatorBest for a first budget before deciding whether to DIY or call a deck contractor.Contractor Quote Comparison CalculatorBest when bids look close but allowances, deposits, and change-order risk are different.Roof Shingle CalculatorBest for rough planning and quote checking, not for walking or measuring a roof.

Quick answers

The numbers people look up most.

Standard assumptions are listed on each calculator page and on the methodology page.

How many gallons of paint for a 12 x 12 room?

About 3 gallons for two coats on the walls with 8 foot ceilings. Paint calculator

How many 80 lb bags of concrete are in a cubic yard?

45 bags. Each 80 lb bag yields about 0.6 cubic feet and a yard is 27 cubic feet. Concrete bag calculator

How many bags of mulch are in a cubic yard?

13.5 bags of 2 cubic foot mulch. One yard covers 108 square feet at 3 inches deep. Mulch and gravel calculator

How much extra flooring should I buy?

10 percent for straight layouts and 15 to 20 percent for diagonal or herringbone. Flooring calculator

How many sheets of drywall for a 12 x 12 room?

About 12 sheets of 4x8 for the walls, or 17 sheets including the ceiling. Drywall calculator

How many bundles of shingles are in a square?

3 bundles for most asphalt shingles. One roofing square is 100 square feet. Roof shingle calculator

Planning guides

Short guides for the choices calculators cannot make.

Waste percentages, bag versus bulk, primer, underlayment, and how to compare contractor quotes. Browse all guides.

Paint planningHow Much Paint Does a Room Need?Paint planningWhen Do You Need Primer and Extra Paint?Paint planningHow Much Does a Gallon of Paint Cover?Paint dataPaint Coverage by Brand: Square Feet per Gallon ComparedLandscape planningMulch Bags vs Cubic Yards: How Many Bags Are in a Yard?Gravel planningHow Deep Should Gravel Be for Paths and Small Pads?Flooring planningHow Many Boxes of Flooring Do I Need?Flooring planningFlooring Underlayment and Transition ChecklistTile planningHow Much Thinset and Grout Do I Need for Tile?Tile planningHow Much Extra Tile to Buy: Waste by LayoutDrywall planningHow Much Drywall, Mud, Tape, and Screws Do I Need?Concrete planningConcrete Bags vs Ready-Mix: When to Order a TruckConcrete planningConcrete Bag Count Mistakes to AvoidFence planningHow Many Fence Posts, Pickets, and Bags of Concrete?Deck planningHow Many Deck Boards and Joists Do I Need?Quote planningHow to Compare Contractor Quotes: A ChecklistRoof planningHow Many Bundles of Shingles in a Square and Per Roof?Roof dataShingle Bundles per Square by Brand: GAF, Owens Corning, IKOStore run planningSmall Home Project Shopping ChecklistQuote sanity checkDIY vs Contractor: Cost and Risk by Project