# Glossary

- Link: https://www.qtywise.com/glossary/
- Published: 2026-09-26T17:56:01-04:00
- Author: Jamie C.

Glossary

# 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 the[tool library](https://www.qtywise.com/#tool-library)
and[planning articles](https://www.qtywise.com/blog/). 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)

[Use the Cfm Calculator](https://www.qtywise.com/hvac/cfm-calculator/)

### 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

[Use the Cfm Calculator](https://www.qtywise.com/hvac/cfm-calculator/)

### 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

[Use the Pool Volume Calculator](https://www.qtywise.com/pools-water-systems/pool-volume-calculator/)

### 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

[Use the Board Foot Calculator](https://www.qtywise.com/framing-lumber-stairs/board-foot-calculator/)

### 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

[Use the Board Foot Calculator](https://www.qtywise.com/framing-lumber-stairs/board-foot-calculator/)

### 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

[Use the Square Footage Calculator](https://www.qtywise.com/general-calculators/square-footage-calculator/)

### Compacted depth

The final layer thickness after compaction. It may require a different loose delivery
volume, depending on the material and installation method.

[Use the Asphalt Calculator](https://www.qtywise.com/landscaping/asphalt-calculator/)

### 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

[Use the Flooring Calculator](https://www.qtywise.com/flooring-tile/flooring-calculator/)

### 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

[Use the Yardage Calculator](https://www.qtywise.com/general-calculators/yardage-calculator/)

### 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

[Use the Pipe Volume Calculator](https://www.qtywise.com/pools-water-systems/pipe-volume-calculator/)

### Datum

A reference plane, line, or point used for a measurement.

### Density

Mass divided by volume for a specified material.

**Formula:** Density = mass ÷ volume

[Use the Concrete Weight Calculator](https://www.qtywise.com/weight-calculators/concrete-weight-calculator/)

### 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.

[Use the Epoxy Calculator](https://www.qtywise.com/walls-paint-ceilings/epoxy-calculator/)

### Fence bay

A section of fencing between neighboring posts. End conditions, gates and corners
affect the final post count.

[Use the Fence Calculator](https://www.qtywise.com/fencing-pavers-retaining-walls/fence-calculator/)

### 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

[Use the Pipe Volume Calculator](https://www.qtywise.com/pools-water-systems/pipe-volume-calculator/)

### 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

[Use the Steel Weight Calculator](https://www.qtywise.com/weight-calculators/steel-weight-calculator/)

### 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

[Use the Drywall Calculator](https://www.qtywise.com/walls-paint-ceilings/drywall-calculator/)

### Nominal joint width

The planned spacing between adjacent tiles or masonry units. Actual joints affect
grout or mortar use.

[Use the Grout Calculator](https://www.qtywise.com/flooring-tile/grout-calculator/)

### 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)

[Use the Gravel Calculator](https://www.qtywise.com/landscaping/gravel-calculator/)

### 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)

[Use the Sakrete Calculator](https://www.qtywise.com/concrete-masonry/sakrete-calculator/)

### 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

[Use the Paint Calculator](https://www.qtywise.com/walls-paint-ceilings/paint-calculator/)

### 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

[Use the Pool Salt Calculator](https://www.qtywise.com/pools-water-systems/pool-salt-calculator/)

### 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)

[Use the Rafter Calculator](https://www.qtywise.com/roofing/rafter-calculator/)

### 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

[Use the Square Footage Calculator](https://www.qtywise.com/general-calculators/square-footage-calculator/)

### Rectangular volume

The space within a rectangular prism, used for slabs, material layers and rectangular
tanks.

**Formula:** Volume = length × width × depth

[Use the Concrete Calculator](https://www.qtywise.com/concrete-masonry/concrete-calculator/)

### 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.

[Use the Wallpaper Calculator](https://www.qtywise.com/walls-paint-ceilings/wallpaper-calculator/)

### 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

[Use the Roof Pitch Calculator](https://www.qtywise.com/roofing/roof-pitch-calculator/)

### Roofing square

A unit of roof surface area equal to 100 square feet.

**Formula:** Roofing squares = roof surface area (ft²) ÷ 100

[Use the Roofing Calculator](https://www.qtywise.com/roofing/roofing-calculator/)

### Roof pitch

Roof slope expressed as rise over horizontal run.

**Formula:** Pitch per 12 units of run = rise ÷ run × 12

[Use the Roof Pitch Calculator](https://www.qtywise.com/roofing/roof-pitch-calculator/)

### 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)

[Use the Roof Pitch Calculator](https://www.qtywise.com/roofing/roof-pitch-calculator/)

### 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

[Use the Stair Calculator](https://www.qtywise.com/framing-lumber-stairs/stair-calculator/)

### 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.

[Use the Tank Volume Calculator](https://www.qtywise.com/pools-water-systems/tank-volume-calculator/)

### 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.

[Use the Tile Calculator](https://www.qtywise.com/flooring-tile/tile-calculator/)

### 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

[Use the Square Footage Calculator](https://www.qtywise.com/general-calculators/square-footage-calculator/)

### 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

[Use the Concrete Calculator](https://www.qtywise.com/concrete-masonry/concrete-calculator/)

### 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 term](https://www.qtywise.com/contact/)and the tool or project where
you encountered it. Include the product wording if the definition depends on a particular
material.