Roof Rainfall Calculator for Biloxi, MS
This free roof rainfall calculator shows how much water your Biloxi, MS roof sheds in a storm and across a year, for homes in 39530, 39530, 39530, 39530, 39530, 39531 and 39532, from Downtown Biloxi to Woolmarket. Enter your roof area to see the gallons your gutters must carry — and why size matters here.
Quick answer: One inch of rain on a 1,800 sq ft Biloxi roof is about 1,120 gallons. Across a Biloxi year — 64 to 65 inches — that same roof sheds roughly 72,300 gallons. Your gutters and downspouts have to move every gallon of it, which is why size and cleaning matter as much as the gutters themselves.
How much water does your roof shed?
Use your roof's footprint — length times width, roughly. A 1,800 sq ft footprint is a typical Biloxi single-story home.
Enter a roof area above zero and a rainfall amount of zero or more.
How this roof rainfall calculator works: roof square feet × inches of rain × 0.623 gallons per square foot per inch of rain. One inch of rain on 1,800 sq ft is about 1,120 gallons. The result also shows gallons per downspout, the per-hour rate in a 1-inch-per-hour downpour, and your sloped roof surface.
From roof area to gallons, step by step
The rainfall math is one chain of multiplications. Follow it once and the calculator's result stops being a black box:
Example: 1,800 sq ft × 1 inch × 0.623 = about 1,120 gallons; across 4 downspouts, about 280 gallons each.
What your result means
Your 1-inch storm number
This is the number to compare against your current system. If your gutters have ever overflowed in ordinary rain, the gap between this number and what your gutters and downspouts can move is your problem, stated in gallons. A 1,800 sq ft roof at 1,120 gallons per inch of rain needs a system that moves that water continuously — not eventually, and not mostly.
Your annual number
The full-year figure — about 72,300 gallons for that same roof — is the workload, not a single event. It explains why a system that looks fine in a dry month fails in a wet one, and why small problems (a sagging run, one clogged downspout) compound across a Biloxi year instead of staying small.
Gallons per downspout
The per-downspout figure is the most actionable number on the page. If each downspout must carry hundreds of gallons in a single storm and you have few of them, adding a downspout can matter as much as upsizing the gutter. Take all three numbers — total, per-downspout, and per-hour — to the size calculator and then to your free measurement.
Biloxi rain, in numbers
Biloxi receives about 64 to 65 inches of rain a year, and hurricane season runs June 1 to November 30. Put those two facts through the calculator and the scale of the job your gutters do becomes concrete. A typical 1,800 sq ft Biloxi roof sheds about 1,120 gallons in a single 1-inch rain, about 5,600 gallons in a 5-inch tropical downpour, and about 72,300 gallons across a full year. None of that water disappears. Every gallon either runs down a downspout and away from the house, or it comes over the gutter edge right next to the foundation.
That is why this calculator sits next to the size calculator on this site. The rainfall number is the demand; the gutter size is the supply. When demand exceeds supply — a big roof, a hard downpour, a gutter narrowed by pine needles — the surplus does not wait politely. It overflows, and it overflows exactly where it does the most damage.
Where all that water goes
A working system moves water in four steps: roof to gutter, gutter to downspout, downspout to grade, grade away from the house. Any step can fail. Gutters pitched the wrong way hold water instead of moving it. Clogged gutters hold water and add weight until they sag. Too few downspouts, or downspouts that end right at the foundation, send thousands of gallons a year into the soil that holds your slab up. The symptoms show up slowly — fascia boards softening, landscaping washing out, dampness near the foundation — and then all at once.
The fix is rarely exotic. Right-sized gutters, the right number of downspouts, correct pitch, and a cleaning rhythm that matches your tree cover will carry a Biloxi year's rain without drama. See our gutter size calculator for the sizing half, and our gutter maintenance page for the cleaning half.
What the numbers mean for your gutters
Use the calculator twice. First, run the 1-inch storm number: if your gutters have ever overflowed in ordinary rain, compare that number with what your current system can carry — the gap is your problem, stated in gallons. Then run the full-year number: that is the annual workload your gutters carry, and it explains why a system that looks fine in a dry month fails in a wet one.
Two upgrades change the math most. Stepping from 5-inch to 6-inch gutters adds about 40–44% more capacity for $1 to $3 extra per linear foot. And keeping gutters clear matters as much as size — a clogged 6-inch gutter carries less than a clean 5-inch one. If pines overhang your roof, read our gutter guards for pine needles guide, and if a storm just passed, our hurricane gutter prep guide covers what to check first.
Rainfall in gallons: storm bars and the year that dwarfs them
For a typical 1,800 sq ft Biloxi roof, the same roof sheds very different water in different events. The bars below are drawn to a single honest scale — which is exactly why the annual figure is shown as a number, not a bar:
All figures for an 1,800 sq ft footprint at 0.623 gallons per square foot per inch of rain. Scale: 5,600 gallons = 560 pixels of bar.
Gallons in a 1-inch rain, by roof size
Find your roof size for the water your gutters must move in a single inch of rain — the unit every Biloxi storm is built from:
| Roof footprint | Gallons in a 1-inch rain | 55-gallon drums |
|---|---|---|
| 1,200 sq ft | 748 | 14 |
| 1,500 sq ft | 935 | 17 |
| 1,800 sq ft | 1,121 | 20 |
| 2,400 sq ft | 1,495 | 27 |
| 3,000 sq ft | 1,869 | 34 |
Multiply any row by the inches in your storm: a 2-inch rain doubles it, a 5-inch tropical downpour multiplies it by five. The calculator above does the same arithmetic for any roof and any rainfall you enter.
Storm-season checklist for Biloxi gutters
Hurricane season runs June 1 to November 30. Work through this list before it opens, and again after any storm that drops serious water:
Before June 1
- Clear every gutter run and downspout — pine needles are the usual blockage on Biloxi lots.
- Check the pitch: standing water in a run means the slope has sagged and needs correcting.
- Confirm downspouts discharge away from the foundation, not beside it.
- Look at the fascia behind the gutter for soft or stained boards.
After a heavy storm
- Walk the gutter line for overflow marks, sagging runs, and separated joints.
- Check beds and soil below the gutter line for fresh washout.
- Clear any storm debris before the next rain — one clogged downspout overloads the rest.
- If you saw overflow, run your numbers through the size calculator before the next storm, not after it.
For the full seasonal routine, see our hurricane gutter prep guide.
How to use your number in 3 steps
- Run your storm number. Enter your roof area and a 1-inch rain. That is the baseline your system must handle without drama.
- Check your size. Take the total and the per-downspout figure to the size calculator and see whether 5-inch or 6-inch — and how many downspouts — your roof actually needs.
- Book the measurement. If you have ever seen overflow, or the per-downspout number surprises you, call (228) 888-8061. The free on-site measurement turns these calculator numbers into a written estimate for a system built for them.
Frequently asked questions
How is the rainfall math calculated?
Gallons = roof square feet × inches of rain × 0.623. The 0.623 is the standard conversion: one inch of rain over one square foot is about 0.623 gallons. So 1,800 sq ft × 1 inch × 0.623 = about 1,120 gallons. The calculator does the same arithmetic for any roof and any rainfall you enter.
Should I enter my roof's footprint or its sloped surface?
Enter the footprint — length times width of the house. Rainfall falls vertically, so the footprint is what catches it. A steep roof sheds water faster than a gentle one, but it does not catch more total rain; speed is a sizing question, covered by the gutter size calculator.
How much rain does Biloxi actually get?
About 64 to 65 inches a year. The calculator uses 64.5 inches, the middle of that range, for its full-year preset. Hurricane season, June 1 to November 30, delivers much of it in heavy bursts rather than spread evenly.
Would a rain barrel solve this?
Only a fraction of it. A standard 55-gallon barrel holds what a 1,800 sq ft roof sheds in about a twentieth of a 1-inch rain. Barrels are fine for garden water, but your gutters still have to carry the other 95% — size and drainage do the real work.
What size gutters do I need for this much water?
Run your numbers through the gutter size calculator: it weighs your roof area, pitch, pine cover, and longest run, and recommends 5-inch or 6-inch with its reasons shown. Most Biloxi homes land on 6-inch, which carries about 40–44% more water than 5-inch.
How many gallons does my roof shed per hour in a downpour?
Multiply your roof area by 0.623 for each inch-per-hour of rainfall rate. A 1,800 sq ft roof in a 1-inch-per-hour downpour sheds about 1,120 gallons per hour; at 2 inches per hour, about 2,240. The calculator now shows this per-hour rate, because peak rate — not the yearly total — is what overwhelms a gutter mid-storm.
Do gutters need to handle the whole year's rain at once?
No. Gutters handle peak rate — the gallons per hour during the hardest rain — while the yearly total shows the system's workload over time. Both numbers matter: the peak rate sizes the gutter, and the yearly total explains why small defects compound across a Biloxi year.
Where should downspouts send all this water?
Away from the foundation, always. Thousands of gallons a year discharged beside the slab saturate the soil that holds it up. Downspouts should carry water to grade that falls away from the house; our downspout installation page covers placement, and the free measurement checks discharge points on site.
Your roof sheds thousands of gallons — make sure your gutters carry them
One call gets you a measurement, straight sizing advice, and a written estimate for a system built for Biloxi rain.
Call (228) 888-8061