How to read a size
Storage unit sizes are written as width by depth in feet. A 5×10 is about five feet wide and ten feet deep, roughly 50 square feet. A 10×10 is about 100 square feet. A 10×20 is about 200, a 10×30 about 300. Those numbers are the floor. They do not tell you the ceiling height, the door width, or whether you can stand a mattress on end. Cove uses the same ladder from 5×5 to 10×30 on the calculator at the unit size calculator and on this page.
The guide is a planning estimate. It maps rooms and a short list of large items onto that ladder, then explains the square feet. It does not know which sizes a facility has vacant, what they cost, or how high the ceiling is. After you have a size, open a city page such as Greenville, SC, Columbia, SC, Spartanburg, SC, or Atlanta, GA and call. Ask for that size, and ask what the total is at move-in.
5×5, 5×10, and 5×15
A 5×5 is the closet size on Cove's guide: boxes, luggage, seasonal clothes, and small furniture. Think of a walk-in closet, not a room you can furnish. Everything is in arm's reach of the door if you pack the back first. It is a poor choice for a mattress and a sofa together.
A 5×10 is about 50 square feet, the large-closet or few-pieces-of-furniture step. A dresser, a few chairs, and a stack of boxes can fit if you measure the depth before you buy shelves. A 5×15 is about 75 square feet. On this guide that is a studio apartment packed carefully: a mattress, a compact sofa or chairs, boxes, and small appliances, with little room to rearrange once the door is shut. If you need to visit one box often, do not bury it.
10×10 and 10×15
A 10×10 is about 100 square feet. Cove's guide describes it as a one-bedroom apartment with room to walk. That means a bedroom's furniture, a living room's main pieces, and kitchen boxes, not a house. The extra width, compared with a 5-foot unit, is what lets you leave a center aisle. Use the aisle. Filling it on move-in day saves a few dollars and costs an hour every time you need something from the back.
A 10×15 is about 150 square feet. On this guide it is the two-bedroom apartment or a small house packed with some care. Two bedroom sets, a sofa, a dining table broken down or stood aside, and kitchen goods can fit. A third bedroom, a large dining set you refuse to take apart, or a washer and dryer you cannot stack on will push you toward a 10×20. The calculator counts rooms you are actually storing. An empty bedroom you are not moving does not count.
10×20, 10×25, and 10×30
A 10×20 is about 200 square feet. Cove's guide calls it a three-bedroom house, or a smaller home plus a motorcycle. The motorcycle matters because it takes floor you cannot stack on. A 10×25 is about 250 square feet, the three- or four-bedroom example. A 10×30 is about 300 square feet, a four-bedroom house or a household plus a car's worth of floor. These are examples of volume, not a rule that every four-bedroom house needs a 10×30. A house full of large furniture needs more than a house full of boxes.
Door height and ceiling height start to matter as soon as the unit is large enough to hold a sofa and a mattress at the same time. Ask whether the door is a swing door or a roll-up, and whether you can stand the mattress up. A unit that is large on paper and short at the door still fails if the sofa will not go in. Ask before you rent a truck.
Square feet you cannot stack on
Some items only use floor. A refrigerator, a washer or dryer, a safe, and a vehicle cannot hold a stack of boxes on top. Cove's calculator treats those as floor. A sofa, a mattress, a dresser, and medium boxes can be stacked or stood up, so they share the height of the unit. If you count a sofa as if it were a pallet of boxes, you will under-size the unit. If you count every box as if nothing can go above it, you will over-size it.
Leave a path. A 10×10 that is packed to the ceiling with no aisle is a 10×10 you cannot use. The practical fit is smaller than the label. Dishes and lamps need padding more than they need a larger unit. Taking furniture apart, photographing the hardware, and keeping a simple inventory taped inside the door will do more for a small unit than renting the next size up and still losing the hardware.
Vehicles, boats, and the sizes that do not apply
A car or small SUV is on the order of 180 square feet of floor in Cove's calculator, which points at a 10×20 before you add household goods. A pickup or large SUV is larger. Many facilities do not allow vehicles in a standard indoor unit at all. Door height, oil drips, and insurance are their rules, not Cove's. Ask. If the answer is no, look at vehicle storage on that city's page rather than forcing the car into a 10×10.
An RV, a travel trailer, or a boat on a trailer is outside this ladder. Do not add its length to a 10×30 and hope. Use an RV and boat storage page, and read how much RV storage costs for the questions that change a quote. If you have both a household and an RV, you may need both products. The calculator will say so when you mark the RV or the boat.
Climate, access, and price are separate from size
A 10×10 that is climate controlled is not the same product as a 10×10 that is a drive-up roll-up door on an outside wall. The floor area matches. The risk to wood, mattresses, and electronics does not. Read climate-controlled versus regular storage before you decide the size is the only question. Cove does not know which listed facilities are climate controlled. You have to ask.
Cove also does not publish a price for any size in any city. A larger unit is not automatically a worse deal if the smaller one forces a second unit or a second trip. Ask each facility for the size you calculated, and for the size on either side of it, and for the total due at move-in. Then compare. What else changes that quote, still without a published rate, is in what affects a storage unit's price. What many facilities refuse to take is in what not to store in a storage unit. The directory at Greenville, SC, Columbia, SC, Spartanburg, SC, and Atlanta, GA is a list of places to call, grouped by city.
A practical way to pick
List the rooms whose contents are going into storage, not the rooms in the house. Add the large items that are not already inside those rooms, including appliances and vehicles. Run the unit size calculator. Read the note it gives you, especially if it splits household goods from a vehicle. Then walk the largest piece through the door in your head: mattress height, sofa depth, and the refrigerator that cannot lie down.
If the result feels tight, step up one size rather than hoping the pack is perfect. If the result is a 10×30 and most of the house is staying, you counted rooms you are not storing. Either way, call two facilities with the same size in mind. Availability is their answer. Cove's answer stops at the estimate and the list of facilities.