About CrunchYourDollars

Why this site exists

Every "what size do I need" calculator online stops at a number. You type in your appliances and get "you need 2,400 watt-hours" or "you need a 48,000 grain softener," and then you are on your own in a sea of listings, half of which do not say whether they can start a well pump or handle iron. The number was never the hard part.

CrunchYourDollars does the second half. Each tool runs your answers against a maintained database of current models with real capacity, output, surge and flow specs, and shows you the two or three that fit, with the reason written out in your own numbers. If nothing portable fits, it says so and tells you what class of equipment you actually need.

How the tools are built

• Load math. Running watts, start-up surge, duty cycle and hours per day come from a shared appliance table based on manufacturer spec sheets, ENERGY STAR data and owner-reported meter readings. You can override any figure in any tool.
• Sizing rules. Battery and power station sizing applies an inverter efficiency factor and a reserve margin. Generator sizing uses the standard "all running loads plus the largest single start-up" method. Water softener sizing uses the Water Quality Association's compensated-hardness adjustment for iron and sizes to about 70 percent of nominal capacity so the unit regenerates efficiently.
• Electricity rates. Running costs use the U.S. Energy Information Administration's 2025 annual average residential price for your state, refreshed each October when EIA publishes final data. Type your own rate from your bill and the tools use that instead.
• Product database. Specs and approximate prices are pulled from manufacturer pages and retailer listings, dated on every card, and refreshed about twice a year. If a spec on this site is wrong, email us and we will fix it.
• Show my math. Every result includes the formula filled in with your inputs so you can check it by hand.

How the site makes money

Some product links are paid links. If you buy through them, the retailer or brand pays us a commission at no cost to you. Each card says whether its link is paid. Commissions do not change the math, the picks or the ranking, and the tool does not know what any link pays. Full details are on the disclosure page. We do not write reviews, we do not assign ratings, and we do not sell leads to installers.

What you will find here

• Generator Size Calculator: Running and starting watts for your outage loads, inverter vs open frame, hookup options, matched models.
• Home Battery Backup Sizer: How many kWh and kW your essential circuits need for a multi-day outage, and which systems fit.
• Power Station Size Calculator: Watt-hours for a CPAP, fridge, camping trip or van, plus how long any unit will run your gear.
• Generator Fuel Calculator: Gallons of gas and tanks of propane per day for 20 generators at your load, and what an outage costs.
• EV Charger Size Calculator: Charger amps for your daily miles, the breaker it needs, monthly charging cost, and chargers that fit your car's plug.
• Off-Grid Solar Calculator: Panel watts, battery size and inverter for a shed, cabin or RV from your daily loads and sun hours.
• Water Softener Size Calculator: Grain capacity from your hardness, iron and household size, then matched systems for city or well water.
• Tankless Water Heater Size Calculator: GPM and BTU from the fixtures you run at once and your groundwater temperature, then heaters that deliver it.
• Whole House Water Filter Size Calculator: Flow rate and port size from your bathrooms, the filter type your water needs, and the yearly cartridge cost.
• Heat Pump Water Heater Calculator: Tank size for your household, yearly savings over your current heater, payback, and whether your space fits one.
• AC BTU Calculator: BTU for any room from the ENERGY STAR chart, what it costs to run, and window or mini-split units that fit.
• Air Purifier Size Calculator: The CADR your room needs, the yearly cost of power and filters, and purifiers that clear it.
• Pool Heat Pump Size Calculator: BTU for your pool and temperature rise, what it costs per hour to run, and heat pumps that fit.
• Dehumidifier Size Calculator: Pints per day for a basement, crawlspace or room, the drain setup that fits, and the monthly cost to run.
• Mini Split Size Calculator: BTU per zone for your rooms and climate, how many heads you need, the heating cost, and DIY or pro-install systems that fit.
• Garage Heater Size Calculator: BTU or watts to warm your garage from its size, insulation and climate, electric vs propane vs gas, and the cost per hour.
• Whole House Fan Size Calculator: CFM from your square feet, the attic vent area it needs, and how much it saves over running the AC.
• Central Air Conditioner Size Calculator: Tons for your home and climate, the SEER2 your region requires, AC or heat pump, and what it costs to run each summer.
• Smart Thermostat Savings Calculator: What a smart thermostat saves on your heating and cooling, and how many months each model takes to pay back.
• Robot Lawn Mower Size Calculator: Rated lawn area, slope and navigation your yard needs, and the robot mowers that fit.
• Robot Vacuum Finder: Whether your home needs LiDAR, a self-emptying dock or a mop, and the robots that have them.
• Robotic Pool Cleaner Finder: Pool robots rated for your pool size and type, with walls, waterline, corded or cordless.
• Cordless Vacuum Finder: The runtime your home needs, anti-tangle brushes for pets, and stick vacuums that deliver.
• Snow Blower Size Calculator: Single, two or three stage and clearing width from your driveway size and snowfall, plus gas or battery.
• Grow Tent and Indoor Greenhouse Sizer: Tent size, grow light watts and fan CFM for your vegetables, herbs or seedlings, and the monthly cost to run.
• Golf Simulator Room Size Calculator: Whether your ceiling clears a driver swing, which launch monitors fit the depth, the screen size and where the projector mounts.
• Aquarium Size and Cost Calculator: Real gallons, filled weight and floor load, filter and reef flow, heater watts and the monthly cost to run any tank.
• Game Room Size Calculator: Which pool table, ping pong, shuffleboard and dart setups fit your room, laid out to scale, plus home bowling lane lengths.
• Home Training Range Planner: Whether your room fits dry fire or a 10 m airgun lane, target scaling, and a pellet trap rated for your airgun.
• Home Theater Size Calculator: Screen size from your seats, projector throw, riser height, the Atmos speaker layout and a receiver that runs it.
• Home Bar and Speakeasy Size Calculator: Bar length for your stools, the room it takes, kegerator taps, ice per party, bar tools and glassware, and the hidden bookcase door size.
• Wine Cellar Calculator: Cooling unit size from your room's cubic feet, how many bottles the walls hold, racks, door seals and the cost to run.
• Sauna Heater Size Calculator: Heater kW from your sauna's cubic feet, glass and walls, the breaker and wire it needs, and the cost per session.
• Home Security Planner: How many cameras, which doorbell, lock and alarm, and whether you need a monthly plan, from your home's layout.
• Appliance Cost to Run Calculator: What any appliance costs per hour, day and month at your state's electricity rate.
• Electricity Rates by State: Every state's average residential rate from the EIA, ranked.

A note on safety and professional work

Sizing is just arithmetic. Installation is another matter. Anything that connects to your electrical panel (interlock kits, transfer switches, smart panels, 240V circuits) must be installed by a licensed electrician and inspected where required. Never run a generator indoors or in a garage, and never backfeed a panel through a dryer or range outlet. Water treatment equipment should be sized from an actual water test.

Get in touch

Spec corrections, models to add, bugs, questions: contact@crunchyourdollars.com.