How Many Sandbags Do I Need to Protect My House?
It is the most common question we get during hurricane and flood season, and the honest answer is: it depends on what you are protecting and how high the water is expected to rise. The good news is the math is straightforward once you know two numbers — the linear feet of opening you need to close off, and the height of water you expect.
This guide walks through the actual math the U.S. Army Corps of Engineers uses in its 2022 Flood Fight Handbook, gives you three real-world worked examples, and shows how StormBag's purpose-built door and garage kits cut the bag count significantly compared to freestanding sandbag walls.
Skip the math. Take our free 60-second StormBag Storm Protection Planner. Answer six quick questions about your home and we will recommend the exact kit or bundle you need. No measuring required.
Or read on to learn how to calculate it yourself.
The Two Numbers You Need
Every flood barrier calculation comes down to:
- Linear feet of opening — the total width of the opening (or perimeter) you are sealing off. Measure with a tape measure. A standard exterior door is about 3 feet wide, the framed opening is closer to 4 feet. A two-car garage door is typically 16 feet wide.
- Barrier height — how tall the wall of bags needs to be. Use the most recent National Weather Service flood forecast for your area, then add 6 inches as a safety factor. Most residential flood events involve 6 to 24 inches of standing water.
USACE notes that 5 feet is the practical maximum height for any sandbag barrier. The preferred ceiling is 3 feet. If you are expecting more than 3 feet of water against your home, evacuation is the right call — no temporary barrier is going to hold that volume safely.
The USACE Sandbag Math (Traditional Sandbags)
For traditional burlap or polypropylene sandbags filled with sand, the U.S. Army Corps of Engineers publishes a standard table. Each bag is roughly 14 by 24 inches, filled two-thirds full, weighing 30 to 40 pounds. The bags are stacked in a pyramid pattern (3 bags wide at the base for every 1 foot of height) so the wall does not topple under water pressure.
Bags required per 100 linear feet of barrier (USACE, 2022):
- 1 foot tall — 600 sandbags
- 2 feet tall — 2,100 sandbags
- 3 feet tall — 4,500 sandbags
- 4 feet tall — 7,800 sandbags
For a single 3-foot doorway protected to 1 foot of water, that is roughly 18 traditional sandbags built freestanding. Scale that to a 16-foot garage at 2 feet of water and you are looking at over 300 traditional sandbags — the equivalent of more than 10,000 pounds of sand and several hours of physical labor.
This is why most municipal sandbag programs limit households to 10 to 25 bags per residence, according to a 2020 FEMA-published study on community sandbag programs. There simply is not enough sand or labor to protect a whole house with traditional bags.
How StormBag Door Kits Change the Math
StormBag is a sandless sandbag — a 1-pound dry bag containing a super-absorbent polymer (SAP) inside a woven polypropylene shell. When you add fresh water, the bag expands in roughly 3 minutes to 33 pounds and absorbs about 4 gallons. See the full technical specs here.
For doors and garage doors, our pre-packed kits are sized using the same USACE-recommended technique of pairing sandbags with a heavy-duty plastic sheet. The plastic creates the watertight surface, the StormBags weight it down and seal the bottom edge. Together you need fewer bags than a freestanding wall to seal the same opening, because the plastic does the sealing work and the bags do the anchoring. Watch our 3-minute deployment video to see how the wall is built.
Each StormBag is also taller per layer than a traditional sandbag, so you reach the necessary height in fewer rows. We covered this in detail in our guide on why barrier height matters more than weight.
StormBag Door Kit Sizing Guide
Each kit ships with the right number of StormBags, the right size of 4-mil plastic sheeting, heavy-duty duct tape, and a box cutter. Just match the kit to your opening:
| Kit | Opening Size | StormBags | Plastic Sheeting | Price |
|---|---|---|---|---|
| Single-Door Kit | 4′ W × 8′ H | 5 | 6′ × 10′ | $69.99 |
| Double-Door Kit | 7′ W × 8′ H | 10 | 10′ × 10′ | $109.99 |
| Single-Wide Garage Kit | 13′ W × 11′ H | 15 | 14′ × 12′ | $149.99 |
| Double-Wide Garage Kit | 21′ W × 11′ H | 25 | 22′ × 12′ | $239.99 |
Full setup instructions are on our how to use StormBag Door Kits page.
Loose StormBags (No Kit) — Use This Math
If you are protecting an opening that does not match a kit (a basement window well, a sliding patio door wider than 7 feet, a side door, or a perimeter section between buildings), use loose StormBags from our 10-pack or 25-pack with a separately purchased plastic sheet.
Loose StormBag count per linear foot, with plastic sheeting:
- Up to 6 inches of water — about 1 StormBag per linear foot (single layer at the base)
- Up to 12 inches of water — about 1.5 StormBags per linear foot (single layer plus weighted seam)
- Up to 18 inches of water — about 2 StormBags per linear foot (double-stacked)
- Up to 24 inches of water — about 3 StormBags per linear foot (double-stacked with extra anchoring)
These are conservative residential estimates that assume slow-onset, slow-velocity flooding (the typical residential scenario — heavy rain, river overflow, storm surge after landfall). For high-velocity flowing water above 6 feet per second, sandbag-style barriers of any kind are not recommended by FEMA's Reduce Flood Risk program.
Three Worked Examples
Example 1: Single Front Door, 12 Inches of Expected Water
A standard front door framed opening is 4 feet wide. The Single-Door Kit is purpose-sized for this exact scenario — 5 StormBags plus a 6′×10′ plastic sheet, $69.99. One kit is the answer.
If you have two doors (front and back), buy two single-door kits or one Double-Door Kit if the doors are close together and you want to consolidate supplies.
Example 2: Two-Car Garage, 18 Inches of Expected Water
A standard two-car garage door is 16 to 21 feet wide. The Double-Wide Garage Kit covers up to 21 feet wide × 11 feet tall — 25 StormBags plus a 22′×12′ plastic sheet, $239.99. One kit handles the entire garage.
Garage doors are also one of the highest-risk entry points because they are wide, often poorly sealed, and built to flex inward under pressure. We cover the full garage protection setup in our sandless vs traditional sandbags guide.
Example 3: Full Single-Story Home, 12 Inches of Expected Water
A typical 1,800 sq ft single-story home has a front door, back door, side door, two-car garage, and a sliding patio door. The simplest bundle:
- 2× Single-Door Kit ($69.99 each) — front and back doors
- 1× Double-Door Kit ($109.99) — sliding patio door
- 1× Double-Wide Garage Kit ($239.99) — two-car garage
Total: 4 kits, 55 StormBags total, $489.96. Side doors and low windows can be covered with extras from a 10-pack of loose StormBags if needed.
This roughly matches USACE Albuquerque District guidance that "most homes and buildings on a concrete slab can be protected with between 25 and 40 sandbags" — and the kit approach uses fewer bags than a USACE freestanding pyramid wall because the plastic sheeting carries most of the sealing load.
Common Mistakes That Cost You Bags (and Money)
- Underestimating the height needed. Add a 6-inch safety factor on top of forecasted water levels. Storm surge and flash floods routinely exceed initial NWS forecasts.
- Skipping the plastic sheet. Loose bags without poly sheeting leak at every seam. The plastic is what makes the seal — the bags weight it down. Our kits include the right size of 4-mil plastic for exactly this reason.
- Hydrating with salt water. StormBags cannot be hydrated in salt water, but they will work to repel salt water once they are hydrated with fresh water. Use tap, hose, rain, pool, or any non-saltwater source for the initial activation. We cover this in detail in our coastal storm surge guide.
- Buying the day before a storm. Shipping windows close 48 to 72 hours before landfall in coastal areas. Buy in May before hurricane season starts, store dry, and you are ready every year. The 30-day NFIP waiting period works the same way — we wrote about that here.
The Easy Way: Use the Planner
Everything above is the "show your work" version. If you would rather just get a kit recommendation in 60 seconds, our planner does the calculation for you.
Take the 60-Second Storm Protection Planner
Answer 6 quick questions about your home. Get a personalized StormBag kit recommendation. No email required.
Or shop the kits directly:
- Single-Door Kit — $69.99 — 4′ doorway, 5 StormBags + plastic + tape
- Double-Door Kit — $109.99 — 7′ double door or sliding patio, 10 StormBags + plastic + tape
- Single-Wide Garage Kit — $149.99 — single-car garage up to 13′, 15 StormBags + plastic + tape
- Double-Wide Garage Kit — $239.99 — two-car garage up to 21′, 25 StormBags + plastic + tape
- Loose StormBags — 10-pack ($99.99) or 25-pack ($239.99) — for windows, basement entries, or non-standard openings
For the full breakdown of how StormBag stacks up against alternatives, see our 2026 best sandless sandbag guide.
