From your space to the right spec
No accounts, no spreadsheets, no sales pitch. Here’s exactly what happens when you use a GearSizer calculator.
Step 1 — Tell us your space
Every calculator asks only for the inputs that actually move the number: a room’s floor area and ceiling height, how damp or sunny it is, or the appliances you need to keep running. It takes about ten seconds, and nothing you enter leaves your browser.
Step 2 — We do the math
Behind each tool is the same standard the manufacturers and pros use — not a guess. Depending on what you’re sizing, that means:
- Air purifiers — CADR (Clean Air Delivery Rate) and the AHAM “2/3 rule,” so you get enough air changes per hour.
- Dehumidifiers — pints of moisture removed per day, scaled to room size and dampness (DOE 2019 method).
- Space heaters — watts of heat output, based on ~10 W per square foot adjusted for insulation and ceiling height.
- Air conditioners — BTUs, starting at 20 per square foot and adjusted for sun, occupants, and kitchens.
- Generators, power stations & UPS — running watts, starting (surge) watts, and watt-hours, added up across the exact appliances you choose.
Step 3 — Buy the right gear
With your number in hand, we show products that actually meet it — matched to your spec, then ranked by rating and value rather than by whichever brand pays the most. Each pick links straight to Amazon, where you’ll always see the current price.
A note on accuracy
Our calculators use industry rules of thumb, which are ideal for choosing a product with confidence. They’re estimates, not a substitute for a professional load calculation on a whole-home system, a permanent standby generator, or an unusual space. When in doubt, size up slightly — it’s cheaper than buying twice.
Ready to get your number?
Pick a calculator and size your gear in under a minute.