Everyday Life & Household 4 calculators
- Heat Index CalculatorNWS Rothfusz heat index regressionThe heat index is what the air temperature feels like once humidity is taken into account, and it is the number that governs…
- Holiday Light String Length CalculatorNEC 2023 (NFPA 70) Article 210 — 80% continuous loadHoliday lighting fails in three ways: you run out of string halfway along the gutter, you trip a breaker on the coldest night…
- Hotel Stay Total Cost CalculatorThe rate a hotel advertises is rarely the rate you pay. A mandatory resort fee, a parking charge you cannot opt out of, a…
- House Cleaning Cost CalculatorLabour-hour estimating with a per-square-foot cross-checkCleaning is quoted two ways — by the hour and by the square foot — and a good quote is the larger of the two…
Insurance & Risk Management 4 calculators
- HDHP vs PPO Total Cost CalculatorIRS Rev. Proc. 2024-25 (2025 HSA/HDHP limits)Premium alone never decides which health plan is cheaper. A high-deductible plan trades a lower premium for a larger bill when…
- Health Plan Total Annual Cost CalculatorACA cost-sharing structure: deductible, coinsurance, out-of-pocket maximumThe cheapest health plan is never the one with the lowest premium, and it is never the one with the lowest deductible either…
- HSA Long-Term Value CalculatorIRC §223 — health savings accountsA health savings account is the only account in the US tax code that is untaxed at all three points: the money goes in without…
- Human Life Value CalculatorHuman life value (Huebner) method — growing annuity present valueHuman life value asks a narrower question than a needs analysis: what is the present value of the earnings a person will…
Agriculture, Livestock & Landscaping 3 calculators
- Hay Needed for Winter CalculatorNRC nutrient requirements (beef, horse, small ruminant)This calculator tells you how many bales and how many tons of hay you must have in the barn to feed a set number of animals for…
- Herbicide per Gallon (Backpack Sprayer) CalculatorFIFRA — the pesticide label is the law (7 U.S.C. §136j)Herbicide labels give you a rate per acre, but a backpack sprayer holds gallons. This calculator bridges the two: enter the…
- Horse Weight & Feed Requirement CalculatorCarroll & Huntington girth-length equation; NRC Nutrient Requirements of Horses (6th rev. ed.)Two measurements — heart girth and body length — estimate a horse's weight closely enough for feeding, conditioning and most…
Computing, IT, Networking & Security 3 calculators
- Hash Collision Probability CalculatorBirthday bound; NIST SP 800-107 Rev. 1A hash or random identifier of b bits has 2 b possible values, but duplicates appear far sooner than that suggests. The…
- HEX, RGB, HSL & CMYK Color ConvertersRGB (IEC 61966-2-1) and CSS Color Module Level 4Give this converter a color in HEX, RGB or HSL and it returns every other notation your tools ask for: six- and eight-digit…
- Hosts per Subnet CalculatorRFC 4632 (CIDR), RFC 3021 (/31 links)Enter a prefix length and this calculator tells you how many addresses the block contains and how many of them you can actually…
Crafts, Textiles, 3D Printing & Photography 3 calculators
- Half Square Triangle (HST) CalculatorQuarter-inch patchwork seam conventionTell this calculator the finished size of the half square triangle you want and it gives you the square to cut, by whichever…
- HTV & Vinyl Roll Usage CalculatorRectangular nesting on a fixed-width rollHeat transfer vinyl is sold by the roll in a fixed width, so the only thing you control is how well the design nests across…
- Hyperfocal Distance CalculatorCircle of confusion = sensor diagonal ÷ 1500 (classic convention)Focus a lens at its hyperfocal distance and everything from half that distance out to infinity records as acceptably sharp. It…
Home Improvement Projects & Renovation 3 calculators
- Home Improvement ROI CalculatorCost-versus-value recoup analysisNo ordinary renovation returns more at resale than it costs. What a good one does is give a large part of the money back, so…
- Home Project Duration CalculatorDeterministic scheduling with explicit floatLabour hours tell you how long the work takes. They tell you nothing about how long the project takes, because a renovation…
- Home Renovation Budget CalculatorLine-item cost estimatingThis calculator turns a renovation into the five lines every estimator uses — materials, labour, fixtures and appliances…
Biology, Genetics & Clinical Lab 2 calculators
- Hardy-Weinberg Equilibrium CalculatorHardy-Weinberg principle (Hardy 1908; Weinberg 1908)Enter how common a recessive phenotype is — as a frequency, as a "1 in N" incidence, or as the allele frequency itself — and…
- Hemocytometer Cell Count CalculatorImproved Neubauer chamber geometryEnter the counts from the four large corner squares of your Neubauer chamber, the dilution you used to load it, and the volume…
Construction, Carpentry & Concrete 2 calculators
- Header & Beam Size CalculatorIRC 2021 R301.5 / R301.6 loads; AWC NDS 2018 allowable stress designThis calculator turns the loads over an opening into a header size. Give it the clear span, the tributary width of roof and…
- Hip & Valley Rafter Length CalculatorEqual-pitch hip and valley geometryGive this calculator the common rafter run and the roof pitch and it returns everything you need to cut a hip or a valley: the…
Energy, Solar, Sustainability & Environment 2 calculators
- Home Battery Backup Sizing CalculatorNEC 2023 Article 706Tell this calculator how much energy your critical loads consume in a day, how long you need to ride through an outage, and how…
- Household Carbon Footprint CalculatorEPA GHG Emission Factors HubA household carbon footprint is a sum of products: each activity multiplied by its emission factor. This calculator does that…
HVAC, Refrigeration & Building Science 2 calculators
- HVAC Delta-T CalculatorASHRAE Fundamentals psychrometrics; furnace nameplate temperature riseThis calculator does two jobs. In cooling mode it takes your return air dry bulb and relative humidity, works out the enthalpy…
- Hydronic GPM Flow Rate CalculatorSensible heat rate equation, ASHRAE Handbook—FundamentalsEnter a heating or cooling load and the temperature drop you are designing around, and this calculator returns the flow the…
Personal Finance, Loans & Credit 2 calculators
- Home Affordability Calculator28/36 and FHA 31/43 debt-to-income guidelinesThis calculator works backwards from your paycheck to a purchase price. It applies the two debt-to-income ceilings underwriters…
- Hourly to Salary CalculatorFLSA (29 U.S.C. §207)Multiplying an hourly rate by 2,080 gives the right answer only for someone who works exactly 40 hours a week, 52 weeks a year…
Physics: Mechanics, Waves & Thermodynamics 2 calculators
- Hooke's Law Spring Force CalculatorHooke's law (linear elastic range)Enter any two of spring rate, deflection and force, and this calculator returns the third from Hooke's law, F = kx . It also…
- Hydrostatic Pressure CalculatorHydrostatic equation P = ρgh; 1 atm = 101,325 Pa exactlyPressure in a still fluid depends only on how far down you are, not on the shape or width of the container. Enter a fluid, a…
Tax, Payroll & Insurance 2 calculators
- Home Office Deduction CalculatorIRC §280A; simplified method under Rev. Proc. 2013-13; Form 8829There are two ways to deduct a home office and they can differ by thousands of dollars. The simplified method pays $5 per…
- HSA Contribution Limit CalculatorIRC §223Your maximum HSA contribution is not simply the headline limit. It is prorated by the number of months you held qualifying…