A helper is a small, explainable process
Each helper has named inputs, visible units, validated ranges, results, explanation steps, and assumptions. It takes the arithmetic out of a familiar task while keeping the process reviewable.
The helpers are practical calculation aids. A material quantity is not a structural design. An electrical relationship is not conductor sizing. A slope calculation does not select a legally required slope.
General construction
Area and volume are the foundation for many estimates. A rectangular area is length × width; a rectangular volume adds a third length. Material helpers can add counts, coverage, and an explicit allowance.
Enter the measured dimensions, not dimensions silently expanded for waste. Keep the allowance as a separate input so the result can show the net amount and the adjusted amount.
Concrete
Slabs: length × width × thickness. Convert all three lengths consistently before multiplying. A four-inch thickness must not become four feet simply because length and width use feet.
Cylinders: circular area × height. The input is a diameter when labeled diameter; radius is half of it.
Bag quantities: divide required volume by the actual yield per bag and round up to a whole bag. Use the yield supplied for the product you intend to buy. Bag weight alone does not specify its mixed yield.
These helpers do not choose a mix, reinforcement, thickness, footing design, or placement method.
Carpentry and framing
Stairs: distinguish total rise, the number of risers, individual riser height, tread depth, and horizontal run. The upper landing convention affects the number of treads. Read it before using the layout.
Framing counts: a basic spacing count is only the starting layout. Corners, openings, end assemblies, blocking, and local requirements can change the purchased quantity.
Board feet: a volume convention using thickness in inches, width in inches, and length in feet. Actual and nominal lumber dimensions are not interchangeable. Use the dimensions appropriate to the purpose of the estimate.
Roofing
Pitch relates rise to horizontal run. The sloped length is the hypotenuse of that triangle. Overhangs, ridge details, birdsmouths, and connection geometry are additional dimensions.
For roof area, know whether the input is a horizontal plan area or a measured sloped area. Applying a slope multiplier to an already sloped measurement counts the slope twice.
Electrical
Basic Ohm’s-law and power helpers show relationships such as current = voltage ÷ resistance. Their stated circuit model matters. A simple DC or resistive calculation does not automatically describe every AC circuit.
Offset geometry can help explain the relationship between an offset height, a bend angle, and the distance between bends. Tool markings, bend radius, and actual fabrication allowances need separate attention.
These results do not choose wire size, breaker rating, conduit fill, protection, or installation requirements.
HVAC
Airflow from a cross-sectional area and an average velocity follows volume flow = area × velocity. A round duct uses the circular area derived from its diameter.
The air-changes helper relates room volume to volume flow per hour. Convert a flow per minute to a flow per hour before dividing by the room volume. The resulting air changes per hour describe a ratio; they do not account for mixing effectiveness, room use, or ventilation requirements.
These helpers do not replace a load calculation or select equipment capacity.
Plumbing
Fall follows horizontal length × slope. A percent slope means a rise or fall per hundred units of horizontal run. A per-foot slope needs the numerator and denominator units converted consistently.
Pipe volume is cylindrical volume using the inside diameter. A nominal pipe size is not necessarily the inside diameter. The result describes geometric capacity, not pressure-rated capacity or a flow prediction.
Before you use a result
- Check the input units and whether the dimensions are measured, nominal, internal, or external.
- Read the assumptions shown by the specific helper.
- Review the steps and the rounding convention.
- Apply project requirements, product instructions, and applicable local rules separately.
The repository’s packages/calculation/docs/FORMULAS.md is the implementation reference for formula sources and test cases. The running app’s helper definition is authoritative for the fields in that build.