KeepCold

How We Calculate and Compare

The calculator is a planning model. It is not a measurement of your refrigerator and not a measurement of a battery. The same function renders the worked example on the calculator page and the numbers below, so the article cannot drift from the code.

Equations

Average watts from an EnergyGuide-style yearly total:

average watts = annual kWh × 1000 / 8760

Average watts from a compressor duty cycle:

average watts = running watts × duty-cycle fraction

Idle is an AC-equivalent allowance, added before inverter loss. It is not applied a second time:

AC-equivalent watts = average watts + idle watts

Runtime and the capacity a duration needs:

runtime hours = capacity Wh × efficiency × (1 − reserve) / AC-equivalent watts

minimum Wh = duration hours × AC-equivalent watts / (efficiency × (1 − reserve))

Defaults are efficiency 0.85, reserve 0.10, and idle 10 W, so runtime = capacity × 0.85 × 0.90 / (average watts + 10). You can change them in the calculator. Efficiency must stay above zero. Reserve must stay below 1. Those two limits are what keep the divisions defined. A zero or negative energy input is rejected instead of being turned into an infinite runtime.

Worked example

500 kWh/year for 24 hours against 2,048 Wh:

  • Average watts: 57.0776
  • AC-equivalent watts (average + 10 W idle): 67.0776
  • Runtime: 23.3568 hours exactly. Rounded to one decimal, about 23.4 hours.
  • Minimum capacity: 2,104.4 Wh

The 2,048 Wh figure is 56.4 Wh under that minimum, so it does not cover the full 24 hours. The comparison tables use the one-decimal runtime, about 23.4 hours, and do not round it to 24.

One station serving two appliances

Average watts from each appliance are added first. Efficiency, the reserve, and the idle allowance are then applied once. Two separate inverter systems would each have their own idle allowance. The combined figure is average energy. It is not both compressors running at the same time, and it is not both startup spikes.

The guide uses a bottom-freezer median of 566 kWh/year plus a chest-freezer median of 218 kWh/year, for 24 hours, at efficiency 0.85, reserve 0.10, and 10 W idle:

  • Combined minimum, full precision: 3,121.497 Wh. Consumer pages round that to 3,121.5 Wh.
  • Adding the two separate minimums counts the idle allowance twice: 3,435.2225 Wh, which rounds to 3,435.2 Wh. That doubled-idle total is not used.

A battery-side idle placement is not used

Adding the 10 W after dividing appliance watts by efficiency would treat idle as already on the battery side. This calculator does not do that. For the same 500 kWh example that unused placement is 23.8911 hours and 2,057.3373 Wh. The pages and the result tables stay on the AC-equivalent allowance above.

Rough style estimate

The first choice, “I just need an estimate,” does not ask for watts, a duty cycle, or a model number. It asks for a style, an optional size, an optional brand, and whether to plan for higher use or an older refrigerator. Brand never changes the kilowatt-hours. The numbers are a snapshot of public ENERGY STAR certified-model rows retrieved on 2026-11-08, not a national average and not a picture of every refrigerator in use.

  • Refrigerator export, 4,930 rows, SHA-256 255b2a6cae5b502b7c0593a2712a3cf5b2aecd512cace0c597e17298d18a8ce3: ENERGY STAR certified residential refrigerators.
  • Freezer export, 680 rows, SHA-256 7168f80de73306b7b05e6f4b53de04c0b51a8dd37d1c2df3aa52a7ca602e5689: ENERGY STAR certified residential freezers.
  • A row is kept when the market includes the United States, ENERGY STAR Compact is not Yes, total volume is at least 7.75 cubic feet, and the type is top freezer, bottom freezer, side-by-side, chest freezer, or upright freezer. The volume floor matches the federal compact definition, total refrigerated volume under 7.75 cubic feet, in 10 CFR 430.2. 2,921 rows remain. Coolers, compact refrigerators, and freezerless refrigerators are not in the estimate.
  • Not sure uses only the refrigerator-freezer rows: top freezer, bottom freezer, and side-by-side. Chest freezers are not the low end of an unknown refrigerator. French door is not a separate type in the export, so that choice uses the bottom-freezer rows and says so.
  • When a group has at least 30 rows, low and high are the 10th and 90th percentiles and typical is the median. Percentile position is (count − 1) × p, with linear interpolation, then rounded to the nearest kWh. Ten percent of the certified rows sit outside each end. A shorter list uses its lowest, median, and highest values instead. The chest list is one of those short lists.
  • Size is optional. Under 18, 18 to just under 22, and 22 cubic feet or more are KeepCold groups, not official classes. A group is used only when it has at least 30 rows. Otherwise the result says size was not used.
  • The battery table uses the median unless “higher use or an older refrigerator” is checked. That choice adds 20 percent to the rounded high certified figure. ENERGY STAR’s refrigerator page says an old refrigerator uses about 20 percent more than a certified model. Using that sentence as an add-on is a KeepCold planning assumption. It is not a count of old refrigerators, and it does not cover every unit. The same add-on on a freezer is only that assumption: the sentence is about refrigerators.
  • The 637 kWh/year Most Efficient recognition cap is not used as a household load. A marketing sentence that a certified top freezer uses about 360 kWh/year, and a DOE example of 363.5 kWh/year for one 18.1 cubic foot top freezer, are close to this snapshot’s top-freezer median. They are not the calculation.

The same planning equations then turn the chosen kilowatt-hour figure into estimated watts, runtime, and minimum capacity. The result lists the lower certified end, the typical figure, the higher certified end, and the higher-use assumption. A higher figure needs more watt-hours and a shorter runtime. It does not claim startup compatibility or a safe food temperature.

How the catalog is ordered

Recommendations use in-stock models first, smallest capacity that meets the watt-hour plan. Preorder models appear only after those, or alone when no in-stock model meets the plan. Out-of-stock models stay on the comparison page. If you entered startup watts, a model whose published surge is below that figure is not treated as confirmed. Neither order is a recommendation to buy, and neither order means the compressor will start.

Manufacturer page notes

Capacity, power, weight, warranty, charging, expansion, and availability were checked on the manufacturer pages on November 10, 2026. Availability is that manual check, not a live stock feed. The comparison pages show the figures and say the products were not tested here.

Jackery Explorer 1000 v2 is listed here at 1,024 Wh. A specifications table on that manufacturer page also shows 1,070 Wh. The November 7 record used 1,070 Wh from that table. This catalog uses 1,024 Wh. That disagreement stays on this page.

Source checks that are not part of the shopping pages

An FTC EnergyGuide topic address checked while the label page was written returned HTTP 404, so that page does not link the missing address. Readers use the sticker on the appliance.

The FTC endorsement guide at FTC's Endorsement Guides: What People Are Asking was requested on November 7, 2026. An earlier response that day was a not-found page. A later response returned HTTP 200 and the guide title. This site does not reproduce the guide. The public rule is the disclosure sentence in the footer.

CDC and FoodSafety.gov were read on November 7, 2026 after an earlier request that day was blocked. USDA’s outage page was read on November 10, 2026. The food-safety pages follow those successful reads and tell readers to follow the live page if it changes. The blocked request is not part of the advice.

What is refused

  • No claim that an energy fit means the refrigerator will run.
  • No startup comparison when startup watts were left blank.
  • No use of average watts or annual kWh as if they were continuous running watts.
  • No price, star rating, or testimonial. Stock status is the November 10 manufacturer-page check, not a live feed.
  • No automatic rewrite of these pages when a manufacturer URL changes. The weekly check only flags the change.

Real efficiency, idle draw, battery age, state of charge, and room temperature will differ from the defaults. Duty cycle is not a fixed property of a freezer. The content boundary for the site is the Google Search spam policies: the pages that exist are the ones that answer a planning question, not extra doorway URLs.

These are estimates. Real runtime depends on your fridge, its age, and how often it's opened.