Generator sizing calculator

How generator wattage is estimated from running and starting loads

Portable and standby generators are sold by continuous watts and often also by surge or starting watts. A practical first-pass estimate for a residential essential-load list is to assume every listed appliance may run at the same time, but only one motor starts at a given moment—the usual practice when you avoid simultaneous compressor restarts. Peak watts equal total running plus that single largest start extra. If a listed starting value is below running, running is used for sizing so a data entry slip cannot shrink capacity. This calculator sums all running_watts for total continuous draw, then finds the maximum start extra where start extra equals starting_watts minus running_watts for each row. Optional safety_factor (default one point two five) multiplies the peak before ceiling to recommended_watts, covering nameplate uncertainty, slightly high voltage drop, and modest future growth. Optional power_factor (default zero point eight) converts recommended watts into recommended_kva so you can compare manufacturers who label units in kilovolt-amperes. When starting_watts is omitted, it defaults to running_watts so resistive loads like heaters and lights do not invent a surge. The response also suggests next_standard_watts from a built-in table of common retail nameplates when one is large enough. Every step is deterministic floating-point arithmetic with stable rounding: identical inputs always produce identical JSON. Missing lists, empty arrays, non-positive running watts, out-of-range safety or power factors, and non-finite numbers fail early with invalid_input and are not charged.

What you send and what you get back

Classic check: refrigerator two hundred running and one thousand two hundred starting, sump pump eight hundred and one thousand three hundred, lights one hundred fifty, modem thirty, default margin—total running one thousand one hundred eighty, max start extra one thousand, peak two thousand one hundred eighty, recommended two thousand seven hundred twenty-five watts after one point two five headroom. Validation failures name the offending field so forms can highlight an empty list or a zero running watt row. Wire the free browser form for homeowners and retail floor staff, then call the identical contract from your backend for bulk job lists. Send one required field and two optional fields. appliances is a non-empty array of objects; each object needs positive running_watts and may include starting_watts and an optional name label. Aliases loads, items, list, and devices are accepted for the array. safety_factor is optional and defaults to one point two five when omitted; when provided it must lie between one and three inclusive. power_factor is optional and defaults to zero point eight; when provided it must be greater than zero and at most one. Numeric strings are accepted the same as JSON numbers. On success the response returns appliance_count, a loads array echoing cleaned name, running_watts, starting_watts, start_extra_watts, and original_index for each row, total_running_watts, max_start_extra_watts, largest_start_appliance, peak_watts, the safety_factor and power_factor used, recommended_watts, recommended_kva, optional next_standard_watts, plus formula, method, and unit_note strings. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.

Where generator sizing shows up in real work

E-commerce configurators and chat agents call the API to map appliance tables into a recommendation that stays identical to the public calculator page. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.