Glossary

Last updated: August 15, 2026

Clear, short definitions of the terms you will meet across our calculators.

Amortization: A repayment schedule that spreads a loan's principal and interest over equal periodic payments so the balance reaches zero at the end of the term.
Amp-hour: A unit of electrical charge capacity, most often used to rate battery storage. A 100 amp-hour battery can supply 100 amps for one hour, or a proportionally smaller current for longer.
Annuity: A series of equal payments made at regular intervals, such as the fixed monthly payments on a loan or a stream of regular deposits into an investment.
APR (Annual Percentage Rate): The yearly cost of borrowing shown as a percentage, including interest and certain fees, which makes it easier to compare loan offers.
APY (Annual Percentage Yield): The yearly rate of return on savings or an investment with compounding included, so it reflects interest earned on interest over a year.
Average: A single value that represents the center of a data set. In everyday use it usually means the mean, though the median and mode are also averages.
Baker's percentage: A recipe-scaling system where every ingredient is expressed as a percentage of the total flour weight, which is always fixed at 100 percent. It lets a baker scale a recipe up or down without recalculating every ingredient from scratch.
Bitumen: The binder used in asphalt paving mixes. Bitumen calculators estimate the weight of the full paving mix from area, depth, and density, not the liquid binder alone.
BMI (Body Mass Index): A screening figure relating weight to height, calculated as weight in kilograms divided by height in metres squared.
BMR (Basal Metabolic Rate): The number of calories the body uses at complete rest to maintain basic functions such as breathing and circulation.
BTU (British Thermal Unit): A unit of heat energy equal to the energy needed to raise one pound of water by one degree Fahrenheit. Used to rate the output of furnaces, water heaters, and other fuel-burning appliances.
Body fat: The share of total body weight made up of fat tissue, usually given as a percentage. It is a separate measure from BMI, which does not distinguish fat from muscle.
Calorie: A unit of energy used to measure the energy in food and the energy the body uses. On nutrition labels, one Calorie equals one kilocalorie.
Circular segment: The area of a circle that lies between a chord and the arc it cuts off. Used to calculate the partial-fill volume of a horizontal cylindrical tank, since the liquid surface forms a chord across the circular cross-section.
Compound interest: Interest calculated on both the original principal and previously earned interest, causing a balance to grow faster over time.
Compounding frequency: How often interest is added to a balance, for example annually, monthly, or daily. More frequent compounding produces slightly higher growth.
Cord (firewood): A stacked-wood volume measure equal to 128 cubic feet, typically a 4-foot by 4-foot by 8-foot stack. Firewood calculators convert stack dimensions into full cords.
Core volume (CMU): The volume of the hollow openings inside a concrete masonry unit (CMU or cinder block), which must be filled with grout or concrete for reinforced or fire-rated wall applications.
Coverage width: The effective installed width of a panel or sheet material once overlap with the adjacent piece is accounted for, which is narrower than the panel's raw edge-to-edge width. Metal roofing panels are ordered by coverage width, not overall width.
Denominator: The bottom number in a fraction, which shows how many equal parts the whole is divided into. In three quarters, the denominator is four.
Density: Mass per unit of volume, such as pounds per cubic foot. Construction calculators use it to convert a measured volume of material into an estimated weight.
Depth of discharge: The percentage of a battery's rated capacity that can safely be used before recharging. Lead-acid batteries are typically limited to 50 percent depth of discharge, while lithium batteries can often go to 80 to 90 percent without shortening battery life.
Dot product (scalar product): A single number found by multiplying the corresponding components of two vectors and summing the results. It measures how much two vectors point in the same direction, and is zero when the vectors are perpendicular.
Equity: The share of an asset that an owner actually holds, after subtracting any debt against it. In ownership terms it is the owned portion of the total, often shown as a percentage.
Feeding ratio: The proportion of starter to fresh flour and water used when refreshing a sourdough starter, written as three numbers such as 1:2:2. A higher ratio of flour and water to starter produces a slower, milder fermentation.
Future value: What an amount of money is expected to be worth at a later date after growth from interest or investment returns is applied.
GD&T (Geometric Dimensioning and Tolerancing): An engineering standard for specifying and controlling how much a manufactured part's features are allowed to vary from their ideal geometry, using symbols such as true position rather than plain plus-or-minus tolerances.
Gear ratio: The ratio between the rotational speed of an input gear or shaft and an output one. Used to convert engine or motor RPM into output speed.
GPM (Gallons Per Minute): A flow rate measure equal to the volume of liquid moving past a point each minute, used to size pumps, pipes, and irrigation systems.
Hazen-Williams coefficient: A roughness rating (commonly written as C) for the interior of a pipe, used in the Hazen-Williams formula to estimate water friction loss. Smoother pipes have a higher C value and lower friction loss.
Head loss: The reduction in fluid pressure caused by friction as liquid moves through a pipe, usually expressed per 100 feet of pipe length.
Inflation: The gradual rise in prices over time, which reduces how much a fixed amount of money can buy. It lowers the real value of future cash.
Leap year: A year with 366 days, adding February 29, that keeps the calendar aligned with the Earth's orbit. It occurs in most years divisible by four.
Lean mass: The weight of everything in the body that is not fat, including muscle, bone, organs, and water. It is the counterpart to body fat when body composition is split in two.
Margin: Profit shown as a share of the selling price: profit divided by sales, times 100. It differs from markup, which divides the same profit by cost instead.
Marginal product: The extra output produced by adding one more unit of an input, such as one additional worker, while holding all other inputs fixed. It typically rises at first, then falls as diminishing returns set in.
Mean: The arithmetic average of a set of numbers: the sum of the values divided by how many values there are.
Median: The middle value of a sorted list of numbers. With an even count, it is the average of the two central values.
Mode: The value that appears most frequently in a data set. A set can have one mode, several, or none.
Numerator: The top number in a fraction, which shows how many equal parts are counted. In three quarters, the numerator is three.
On-center spacing: The distance measured from the center of one framing member (such as a stud or joist) to the center of the next, used to calculate how many are needed for a given length.
Percentage: A way of expressing a number as a part of 100. The word means per hundred, so 25 percent is 25 out of every 100.
Percentage point: The plain difference between two percentages. A rise from 10 percent to 15 percent is 5 percentage points, though it is a 50 percent increase.
Percentile: A value below which a given share of a data set falls. Scoring in the 90th percentile means 90 percent of results are at or below yours.
Pitch (roofing): A roof's steepness, expressed as inches of rise for every 12 inches of run. Used to calculate rafter length and total roof surface area.
Power factor: The ratio of usable (real) power to total (apparent) power in an electrical circuit, used when converting between watts and amps.
Principal: The original amount of a loan or investment, before interest is applied.
Proportion: The share of a whole that one part represents, often expressed as a fraction, percentage, or ratio against the total. Baker's percentages express every ingredient as a proportion of the total flour weight.
Range: The difference between the largest and smallest values in a data set, indicating how spread out the values are.
Ratio: A comparison of two quantities that shows how much of one there is relative to the other, often written with a colon such as 3:1.
Regulation innings: The standard number of innings used as the basis for a per-game statistic such as earned run average. Baseball uses 9 innings; most softball leagues use 7, which changes the ERA calculation even for an identical performance.
RMS (Root Mean Square): The effective value of a varying quantity such as an AC voltage or current, found by squaring each value, averaging the squares, and taking the square root. For a sine wave, RMS equals the peak value divided by the square root of 2.
SFM (Surface Feet per Minute): A machining measure of how fast a cutting tool moves across a workpiece surface, calculated from spindle RPM and workpiece or tool diameter.
Simple interest: Interest calculated only on the original principal, not on interest already earned. It produces slower growth than compound interest.
Standard deviation: A measure of how spread out values in a data set are from the mean. A small standard deviation means values cluster close to the average; a large one means they are widely scattered.
Standard normal distribution: A normal (bell curve) distribution with a mean of 0 and a standard deviation of 1. Any normal distribution's values can be converted to it (a z-score) to look up probabilities from a single standard table.
TDEE (Total Daily Energy Expenditure): An estimate of the total calories a person burns in a day, found by multiplying BMR by an activity factor.
True position: A geometric dimensioning and tolerancing (GD&T) measure of how far a feature's actual location deviates from its intended position, expressed as a single tolerance value.
Water hardness (GPG): A measure of dissolved calcium and magnesium in water, expressed in grains per gallon (GPG). One GPG equals 17.1 parts per million (ppm). Water softener sizing uses this figure to calculate daily grain load.
Watt-hour: A unit of electrical energy equal to one watt of power sustained for one hour. It measures total energy delivered or stored, distinct from watts, which measure the rate of power at a single instant.
Z-score: The number of standard deviations a value sits from the mean of its distribution. A z-score of 2 means the value is two standard deviations above average; z-scores let different normal distributions be compared on one common scale.
Boone & Crockett score: A scoring system used by hunting organizations to measure the size and symmetry of antlers, based on the length of the main beams, tines, and mass circumferences, minus deductions for asymmetry between the left and right sides.
Ballast weight: In scuba diving, the amount of lead weight a diver wears to counteract the buoyancy of their body, wetsuit, and gear, so they can achieve neutral buoyancy underwater.
Decathlon scoring: The IAAF point system that converts times and distances from ten different track and field events into a single comparable score, using event-specific constants in a standardized formula.
OPS (On-base Plus Slugging): A baseball statistic that adds on-base percentage and slugging percentage together, combining a hitter's ability to reach base with their power at the plate into one number.
Slugging percentage: A baseball statistic measuring hitting power, calculated by dividing total bases (weighted by hit type) by official at-bats. Unlike batting average, it rewards extra-base hits more than singles.
Split (rowing): In indoor rowing, the time it takes to cover 500 meters at a given pace, used to compare effort and speed on an ergometer independent of total distance rowed.