Project terms, explained clearly.
Quick definitions for the measurements and materials used while planning a project.
How should you use this glossary?
Check the meaning of a term before entering a measurement or comparing products. Area describes a surface; volume includes depth; weight also depends on density. Coverage and yield explain what a particular product can supply.
Use these definitions alongside thetool libraryandplanning articles. Product specifications and local requirements provide the details for your particular project.
Key terms
Air changes per hour
The number of times an airflow equivalent to a room’s volume passes through the room in one hour. The required rate depends on the use and ventilation design.
Airflow from duct velocity
Volumetric airflow derived from duct cross-sectional area and average air velocity. Area and velocity must use compatible units.
Formula: CFM = duct area (ft²) × average velocity (ft/min)
Airflow from room volume
Airflow calculated from a specified air-change rate and room volume. This arithmetic does not determine which ventilation rate a room requires.
Formula: CFM = room volume (ft³) × air changes per hour ÷ 60
Area
The size of a surface, measured in square units. A rectangle’s area equals length multiplied by width.
Average depth
A representative depth used when a vessel has both shallow and deep portions.
Formula: For a constant-width pool with a uniformly sloping floor: average depth = (shallow depth + deep depth) ÷ 2
Base layer
A prepared supporting layer placed beneath a finished surface.
Bedding sand
A leveling layer installed between a paver base and pavers.
Board foot
Lumber volume equal to a board one foot square and one inch thick.
Formula: 1 board foot = 144 cubic inches = 1/12 cubic foot
Board footage
A lumber volume expressed in board feet. Use actual measured dimensions when calculating physical volume.
Formula: Board feet = thickness (in) × width (in) × length (ft) × pieces ÷ 12
BTU
British thermal unit, a measure of heat energy.
Bulk density
The mass of a bulk material divided by its total volume, including spaces between particles. Use the supplier’s figure when converting loose aggregate volume to weight.
CFM
Cubic feet per minute, a measure of airflow.
Circular area
The surface area within a circle. Radius is half the diameter.
Formula: Area = π × radius²
Compacted depth
The final layer thickness after compaction. It may require a different loose delivery volume, depending on the material and installation method.
Compaction
The reduction in air spaces as soil or aggregate is pressed into a denser layer.
Contingency
Money reserved for defined uncertainty or unforeseen project costs.
Coverage
The area a stated amount of product is expected to cover.
Formula: Required units = required area ÷ coverage per unit
Coverage rate
The area covered per unit of product under stated conditions, such as square feet per gallon or square meters per pack.
Cubic yard
A volume equal to 27 cubic feet.
Formula: Cubic yards = cubic feet ÷ 27
Cylinder volume
The internal volume of a cylinder when its radius and length are known. For a pipe, use the inside radius.
Formula: Volume = π × inside radius² × length
Datum
A reference plane, line, or point used for a measurement.
Density
Mass divided by volume for a specified material.
Formula: Density = mass ÷ volume
Dry film thickness
The thickness of a cured coating. It can differ from applied wet thickness because some products lose solvent or water while curing.
Fence bay
A section of fencing between neighboring posts. End conditions, gates and corners affect the final post count.
Flow rate
The volume of fluid moving through a system per unit of time.
Gallons
A unit of liquid volume; distinguish US and imperial gallons.
Grout
Material filling joints between tiles or masonry units.
Inside diameter
The diameter measured across the inside of a pipe or circular opening. Pipe volume calculations use the inside diameter.
Formula: Inside diameter = outside diameter − 2 × wall thickness
Joist
A horizontal structural member supporting a floor or ceiling.
Linear foot
A length of one foot, used for trim, fence runs and other materials sold by length rather than area.
Masonry
Construction using individual units such as bricks, blocks or stone, often joined with mortar.
Material mass
The mass estimated from material volume and a suitable density. For loose aggregate, use bulk density.
Formula: Mass = volume × density
Mortar
A binder used to bed and join masonry units. Bag yield depends on the product, joint dimensions and masonry unit size.
Net surface area
The area left after subtracting openings or other excluded surfaces. Only subtract openings that the ordering method allows.
Formula: Net area = gross area − excluded area
Nominal joint width
The planned spacing between adjacent tiles or masonry units. Actual joints affect grout or mortar use.
Nominal size
A product’s named size, which may differ from its actual measured dimensions. Confirm actual dimensions before calculating coverage or volume.
On-center spacing
The distance from the center of one repeated member to the center of the next, used for studs, joists, rafters and reinforcing bars.
Ordering allowance
An explicitly chosen percentage added to a measured quantity for expected losses or project requirements. It is separate from package rounding.
Formula: Adjusted quantity = measured quantity × (1 + allowance ÷ 100)
Ordering quantity
The amount to purchase after accounting for measured need, allowances and whole package sizes.
Package count
The whole number of packages needed when the required quantity and usable amount per package are known.
Formula: Packages = round up(required quantity ÷ usable quantity per package)
Paint quantity
The paint volume estimated from area, planned coats and the coverage of the selected product.
Formula: Paint volume = paintable area × coats ÷ coverage per unit
Part per million
A concentration unit abbreviated ppm. In dilute water solutions, one ppm is approximately one milligram per liter.
Pitch circle
The circle through the centers of an equally spaced bolt pattern.
Pool salt addition
The mass of salt estimated from a required concentration increase. The target must come from the pool system guidance; this formula assumes a well-mixed pool and ignores salt loss.
Formula: Salt (kg) ≈ pool volume (L) × increase (ppm) ÷ 1,000,000
R-value
A measure of resistance to heat flow.
Rafter
A sloped structural member supporting a roof.
Rafter line length
The geometric sloped length derived from horizontal run and vertical rise. Seat cuts, overhangs and construction allowances require separate treatment.
Formula: Line length = √(run² + rise²)
Rebar
Steel reinforcing bar placed in concrete.
Rectangular area
The surface area of a rectangle, using length and width measured in the same unit.
Formula: Area = length × width
Rectangular volume
The space within a rectangular prism, used for slabs, material layers and rectangular tanks.
Formula: Volume = length × width × depth
Relative humidity
The amount of water vapor in air expressed as a percentage of the saturation level at the same temperature.
Rise
The vertical distance in a slope or stair step.
Roll coverage
The usable area covered by one wallpaper roll after accounting for its dimensions, pattern matching and cuts.
Roof angle
The angle between a roof slope and the horizontal, distinct from a rise-to-run ratio.
Formula: Angle in degrees = arctan(rise ÷ run) × 180 ÷ π
Roofing square
A unit of roof surface area equal to 100 square feet.
Formula: Roofing squares = roof surface area (ft²) ÷ 100
Roof pitch
Roof slope expressed as rise over horizontal run.
Formula: Pitch per 12 units of run = rise ÷ run × 12
Roof slope factor
The ratio of sloped roof length to horizontal run for a uniform pitch. Applying it to plan area assumes that the measured roof follows that pitch.
Formula: Slope factor = √(1 + (rise ÷ run)²)
Run
The horizontal distance used with rise to describe a slope or stair.
Scope of work
The specific tasks, materials, and boundaries included in a project.
Sealant joint
A joint filled with a flexible sealant to accommodate movement or resist moisture, rather than a rigid grout filling.
Sensible heat
Heat that changes temperature without changing a material’s phase, such as warming air without evaporating water.
Soffit
The finished underside of a roof overhang.
Square foot
An area measuring one foot by one foot.
Stair riser height
The vertical height of one step. Dividing total rise by an integer riser count gives the proposed uniform riser height.
Formula: Riser height = total rise ÷ number of risers
Stud
A vertical framing member in a wall that supports the wall assembly and provides fixing points for finishes.
Subfloor
The structural layer beneath finished flooring.
Surcharge
An additional load applied above or behind a retaining wall.
Tank capacity
The internal volume a vessel can hold. Nominal capacity can differ from usable volume or the volume at a partial fill level.
Taper
A steady change in thickness or diameter along a length.
Tile module
The repeated size of a tile plus its planned joint, used when estimating a layout or repeated tile count.
Tonnage
A weight unit or, in HVAC, a measure of cooling capacity.
Topsoil
The upper soil layer used to support plant growth.
Tread
The surface of a stair step that you stand on. Tread depth and stair going are related measurements but can differ when a nosing projects.
Triangular area
The surface area of a triangle. Height is measured perpendicular to its base.
Formula: Area = base × perpendicular height ÷ 2
Truss
An assembly of connected members that carries loads through a planned structural arrangement. A quantity calculator does not establish its load capacity.
Underlayment
A layer installed beneath the finished roof covering.
Unit price
The cost per measurable unit of material or work.
Formula: Material cost = quantity × price per unit
Volume
The space a material or vessel occupies, measured in cubic units. A rectangular volume equals length × width × depth.
Wall thickness
The distance between the inside and outside surface of a pipe or tube.
Waste allowance
Extra material allowed for cuts, breakage, and installation loss.
Wet bulb
A temperature reading influenced by evaporation and air moisture.
Yield
The usable volume or coverage produced by a specified package or batch.
Which measurements are easy to mix up?
- Area and volume:flooring needs an area; a gravel layer also needs a depth.
- Rise and run:rise is vertical and run is horizontal.
- Coverage and yield:coverage usually describes a surface area, while yield can describe usable volume.
- US and imperial gallons:these are different units; choose the unit used by your tank or pool specification.
- Nominal and actual sizes:a product label may name a size that differs from its measured dimensions.
Need a term explained?
Send us the termand the tool or project where you encountered it. Include the product wording if the definition depends on a particular material.