What this calculator does
When water covers a floor, the first question people ask is how much of it there is. It is a fair question, because the volume tells you whether a wet vacuum and towels can handle it, whether you need a pump and whether the weight on the floor or in a ceiling is something to worry about. The calculator above multiplies the floor area of each wet room by the average depth of the water, converts the result to gallons and adds up the rooms. It also shows liters, pounds and the number of bathtubs the water would fill, which many people find a more useful picture than a gallon count.
The math behind it is simple. Floor area in square feet, multiplied by depth in inches and divided by twelve, gives cubic feet of water. One cubic foot holds about 7.48 gallons, and a gallon of water weighs about 8.34 pounds. A hallway that is twelve feet long and four feet wide with half an inch of water on it holds roughly 20 gallons. A twelve-by-ten living room with the same half inch holds about 37 gallons, close to one full bathtub.
How to measure the room and the depth
Use a tape measure for length and width of the wet area. If the water covers only part of a room, measure the wet part, not the whole room. For an odd shape, break it into rectangles and add each one as its own row, so the calculator can treat them separately.
Depth is the number people guess at, and it is the one that matters most, because the result scales directly with it. Water that looks deep is often much shallower than it seems. A ruler or tape measure laid flat on the floor with the end in the water gives a reading in inches. Take a few readings in different places, since most floors are not perfectly level, and use the average. Water on a slab home usually pools toward a low corner or a floor drain, so the depth at one edge can be an inch while the other edge is a thin film. If the water is only a sheen on the surface, use a very small number, such as a tenth of an inch, rather than zero.
What the number tells you
A very small volume, under about thirty gallons, is something a household wet-dry vacuum and towels can usually remove in an hour or two. The standing water is not the end of the job, though, because the more important question is what the water soaked into. Carpet, pad, baseboards and the bottoms of walls hold far more water than the surface, and that absorbed water does not show up in this calculator.
A medium volume, from about thirty to three hundred gallons, is more than a small vacuum can handle comfortably. It is the range where a pump or a commercial extractor makes a large difference in time and in how much water has the chance to soak in. A large volume, several hundred gallons or more, means a lot of weight and a lot of spread. At that point, it is worth shutting off the water and power and calling for help before you do more.
None of these ranges are strict rules. They are rough guides, and your own situation, from the kind of flooring to whether the water is clean, matters more than the number.
What the calculator cannot tell you
The calculator counts only the water standing on the surface. It does not count water that has already soaked into drywall, insulation, carpet, wood or the slab, and in most losses that hidden water is the larger share. It does not account for furniture that displaces water, or for a floor that slopes so that the depth changes across the room. It also says nothing about the kind of water. Clean water from a supply line behaves very differently from water that has come from a sewage backup or from outside, and the safety steps are different.
Think of the result as a way to size the surface problem, not the whole loss. To find the hidden water, you need moisture readings and a thermal camera. That is the work we describe on our moisture mapping page, and it is the reason a puddle that looks small can hide a wet wall.
What to do with the result
If the result is small and the water is clean, remove it quickly with a wet vacuum, lift anything that holds moisture off the floor, and then look closely at the baseboards and the lower few inches of the walls. If the walls feel cool, damp or soft, or if the water ran for more than a few hours, you will likely need professional drying. Our guide to what to do after a water leak walks through the first hour in order.
If the result is larger, or if the water came from a burst pipe, a water heater or a backup, treat it as an emergency. Shut off the water, stay out of any area where water is near outlets, and call. We explain what happens next in emergency water extraction and structural drying. If a water heater was the source, see water heater flood cleanup.
Why weight matters
Water is heavy. Five hundred gallons weighs more than two tons, and that matters in two places. On a floor, it is rarely a problem in a single-story slab home, but in a two-story house or a condo, water on an upper floor puts weight on the ceiling below. Wet drywall and insulation in a ceiling are also heavy, and a ceiling that bulges can fail without warning. If you see a bulge or a sag, keep people out from under it.
The weight also explains why professional crews pump rather than carry water, and why we are careful about how we move equipment and contents in a wet house.
Questions
Why does the calculator ask for depth in inches?
Because most household water losses are shallow, and inches give a more precise result than feet. You can enter a fraction, such as 0.25 for a quarter inch.
Does it work for a basement or a flooded yard?
It works for any flat area where you can measure length, width and average depth, but it was designed with indoor floors in mind. Outdoor flooding is usually not clean water, and it should be handled with care.
Is the result an estimate or an exact figure?
An estimate. It depends on how well you measured the depth and the area, and it does not count water that has soaked into materials.
Should I use this to decide whether to call someone?
It can help, but it is not the only factor. If you are unsure, or if the water came from a source you cannot stop, call. Send us the details and we will tell you what we would need to see.