Why cubic feet per person is a weak starting point
The figure everybody repeats is four to six cubic feet of fresh food space per adult. It is not wrong so much as incomplete, because it treats the refrigerator as storage for a person rather than as a buffer between shopping trips. Two households of the same size can differ by half again in the volume they need, and the variable that separates them is how often food comes into the house.
A household that stops at a shop most days is holding two days of food at any moment. A household that does one large run every fortnight is holding fourteen days of it, and for the first three days after that run the refrigerator is at capacity with things stacked on things. That is the situation the appliance has to be sized for, not the average Tuesday. This calculator applies a multiplier for shopping frequency and a second one for how much of the food arrives raw, because raw ingredients occupy far more volume per meal than the packaged equivalent.
The second thing the per-person figure hides is that fresh and frozen do not scale together. A household that batch cooks or buys meat in bulk can need double the freezer volume of an identical household that does not, while needing exactly the same fresh food space. Sizing them as one number is how people end up with a large refrigerator and a freezer that is full by Wednesday.
Rated volume against usable volume
The cubic feet on the specification sheet is the gross interior, measured as if the cabinet were an empty box. It is measured consistently, so it is a fair basis for comparing one unit against another, and it is not what you can put food in. Shelves take thickness, bins have walls, door trays are already counted in the total, and the last few inches at the back of a shelf are where things go to be forgotten.
| Where the rated volume goes | Effect |
|---|---|
| Shelf and bin material | A few percent, more in a unit with many small compartments |
| Air paths from the evaporator | Real and non-negotiable — blocking them creates warm spots |
| Awkward geometry around a dispenser or ice maker | Can remove a surprising slice from one door |
| The tall bottle that stops a shelf being usable | Not in any specification, always in your kitchen |
Three quarters is the default here and it is deliberately a round number rather than a measured one. If you want it exact for a particular unit, the honest method is to look at the interior in a showroom with a tape rather than to trust anyone's percentage, including this one.
The full freezer question, answered properly
Two claims circulate about keeping a freezer full and only one of them holds up. The claim that a full freezer costs meaningfully less to run is weak. Once the contents are down to temperature, the compressor is not fighting the mass; it is fighting heat leaking in through the walls and door seals and the warm air that comes in when the door opens. A full cabinet loses slightly less air on a door opening, and that is a small effect on a bill.
The claim that a full freezer holds temperature far longer without power is straightforwardly true and it is the reason to do it. Frozen food is thermal mass. Every pound of it has to absorb a substantial amount of heat before it will rise above freezing, and it absorbs that heat from the air in the cabinet, which is what keeps the rest of the load cold. An empty freezer has nothing but air to buffer with, and air has almost no heat capacity by volume. The figures commonly cited by food safety authorities are about 48 hours for a full freezer with the door kept closed and about 24 for a half-full one, with a refrigerator compartment holding roughly four hours regardless.
Filling empty space with jugs of water gets the same effect for the price of the containers. One cubic foot of space takes about 7.5 gallons, so a third of a 15 cubic foot freezer is around 37 gallons, which is a lot of containers and worth doing in stages. Leave headspace in each one because water expands when it freezes, keep them clear of the vents where the cold air enters, and freeze them a few at a time so you are not asking the appliance to remove that much heat in one night. They double as drinking water when the power is out.
Choosing the shape once you have the number
Volume tells you how much and says nothing about layout, and layout is what determines whether a large refrigerator is annoying. A chest freezer holds more per cubic foot of floor space and holds temperature longer when opened, because cold air is dense and stays in the box, but everything is stacked and the bottom layer is archaeology. An upright is easier to use and loses more air every time it opens. A refrigerator with the freezer on the bottom puts the things you touch daily at eye level. A side-by-side gives narrow shelves in both halves and defeats a sheet pan or a large platter.
Physical fit is a separate question from volume and is worth settling before anything else, because the biggest unit that fits your alcove may be smaller than the one this page suggests. Run the alcove, the door swing and the route in through the appliance clearance calculator first. Counter-depth models in particular trade several cubic feet for a flush front, which is a fair trade if you know you are making it.
Once a unit is chosen, its own figures are what matter for cost. Put the nameplate and your electricity rate into the appliance running cost calculator, and if the old unit is still working and living in a garage as a drinks fridge, put that one in as well — a second refrigerator in an unconditioned space is one of the larger silent line items in a household, and the home energy audit guide covers where the rest of them hide.
Questions people ask
What size refrigerator does a family of four need?
Using the defaults on this page, two adults and two children come out around 15 to 17 cubic feet of usable space for weekly shopping and mixed cooking, which points at roughly 20 to 23 cubic feet of rated volume. Shift the shopping to a fortnightly run and cooking to mostly from scratch and the same family lands closer to 22 usable and 29 rated. That spread is the honest answer to the question, and it is why the calculator asks about the pattern rather than handing you a number for a family of four.
Does a bigger refrigerator cost much more to run?
More, but usually less than people expect per cubic foot, because the losses that dominate are through the walls and the door seals and a larger cabinet has proportionally less surface area per unit of volume. What changes the running cost far more than size is the configuration, the age, the condition of the door gaskets and where the unit lives. A refrigerator in a hot garage works considerably harder than the same unit in a conditioned kitchen. The way to settle it for two specific units is to compare their published annual consumption figures against each other and price both with your own electricity rate.
Is a separate chest freezer worth it over a larger refrigerator-freezer?
It depends on whether your freezer demand is bursty. If food arrives in bulk once or twice a year, or you batch cook, a separate freezer is usually the better buy: it holds more per dollar and per square foot of floor, it holds temperature much longer when opened or when the power fails, and it leaves the kitchen appliance sized for daily use. If your freezer holds a bag of peas and some ice, a separate unit is an appliance running all year to store very little, which is the worst outcome on this page. The test is whether it will be more than half full most of the year.
How long will my food stay frozen in a power cut?
The figures commonly cited are about 48 hours for a full freezer and about 24 for a half-full one, with a refrigerator compartment at roughly four hours, all with the door kept shut. Kept shut is doing the work in that sentence: every opening dumps the buffered cold and resets the clock unfavourably. Ambient temperature matters too, so a freezer in a cold basement outlasts one in a warm kitchen. Judge food by whether it still contains ice crystals rather than by the hours on the clock, and when the answer is not obvious, the safe call is the one that costs you the food.
Should I put water jugs in the empty space?
Yes, and it is the cheapest thing on this page. Empty volume is the enemy of hold time, and water is free thermal mass. Leave an inch or two of headspace in every container because water expands as it freezes and a full sealed jug will split. Do not stack them against the vents where the cold air enters the cabinet, freeze them in batches rather than all at once, and label them so nobody counts them as food. In an outage they thaw slowly, keep the load cold while they do it, and then you have drinking water.