How to estimate material without over-ordering
Measure the area first, then convert. The Square Footage Calculator handles the base area for almost any job, and the Square Feet to Cubic Yards Calculator turns that into volume once you add a depth — the step where most bulk-material mistakes happen.
From there use the material-specific tool: the Concrete Calculator for slabs and footings, the Gravel Calculator for driveways and base layers, and the Mulch Calculator for beds. Add roughly 5-10% waste for cut-offs; add more if the shape is irregular, and round up to whole bags or whole yards at the end.
Which calculator do I need for an interior renovation?
Interior work splits into surfaces and framing. For surfaces, the Drywall Calculator converts wall area into sheets, the Paint Calculator into gallons per coat, and the Flooring Calculator or Tile Calculator into boxes with a waste factor built in.
For framing and trim, the Stud Calculator gives stud count and plate lumber at your chosen spacing, and the Baseboard Calculator totals linear feet around a room. Subtract door and window openings from wall area before you buy sheets, but not before you buy paint — edges eat more than you expect.
When roof and slope numbers matter more than area
Anything on an incline is bigger than its footprint, and that catches people out. The Roof Pitch Calculator converts rise-over-run into an angle and a slope multiplier, which you apply before ordering with the Roof Shingle Calculator. A 6/12 pitch roof has about 12% more surface than the ground area beneath it.
Slope also governs safety and drainage. The Elevation Grade Calculator gives grade as a percentage and an angle, and the Ramp Calculator checks that a ramp length meets a usable gradient. For steps, the Stair Calculator keeps riser heights even, which is what makes a staircase feel right underfoot.
Frequently asked questions
- How many bags of concrete do I need for a slab?
- Work out the volume in cubic feet — length times width times thickness — then divide by the yield printed on the bag, usually around 0.45 cubic feet for an 80 lb bag. For anything over roughly a cubic yard, ready-mix delivery is normally cheaper and far less work than mixing bags.
- How much waste should I add to a material order?
- Add about 10% for tile, flooring and shingles, and 5% for sheet goods like drywall on simple rectangular rooms. Diagonal layouts, patterned tile and rooms with many angles push waste toward 15%.
- How do I convert square feet to cubic yards?
- Multiply the area in square feet by the depth in feet to get cubic feet, then divide by 27. A 100 sq ft bed at 3 inches deep is 100 × 0.25 ÷ 27, about 0.93 cubic yards.
- What roof pitch is considered steep?
- Anything above 6/12 is generally treated as steep and above 9/12 usually requires roof jacks or staging to work safely. Steeper pitches also need more material for the same footprint and often carry a labour surcharge.
- How much does a gallon of paint cover?
- Around 350-400 square feet per coat on a smooth, previously painted surface. Bare drywall, textured walls and dark-to-light colour changes drop that significantly and usually need two coats.