Sandbag Calculator: How Many Sandbags Do I Need?
The exact StormBag count for your door, garage, or perimeter
Enter the width of what you're protecting and how high the water is expected to rise. We use the U.S. Army Corps of Engineers formulas and recommend the exact StormBag kit — no measuring tape required.
1. What are you protecting?
StormBag Single-Door Kit
How this calculator works
We use the same formula the U.S. Army Corps of Engineers publishes in its 2022 Flood Fight Handbook, then adjust for StormBag's real-world stacking geometry. Every hydrated StormBag is about 14 in. long × 8 in. wide × 4 in. tall, weighs 33 lb, and interlocks with its neighbors when stacked.
- Bags per row = ceiling(linear feet ÷ 1.17 ft per bag)
- Number of rows = ceiling(water height in inches ÷ 4 in. per bag)
- Base multiplier = for barriers over 12 in. high, add a second row at the base for stability, per USACE stacking guidance
- Overage = 10% added for corners, cut ends, and one spare row on top for freeboard
For a single 3-ft door protected to 12 in. of water, that works out to 3 bags per row × 3 rows × 1.10 overage ≈ 10 StormBags for a freestanding wall — but our Single-Door Kit is engineered to seal the doorway with 18 bags including full jamb-to-jamb coverage and the stability wrap at the sides.
Not sure how tall to build the barrier?
Start with the National Weather Service's local flood forecast for your ZIP code — our Flood Watch page aggregates every active watch, warning, and advisory in the country. Add 6 inches to the forecast crest as a safety factor. If you're expecting more than 36 in. of water against your home, a temporary sandbag barrier is not the right answer — evacuate and consult your local emergency management office. USACE guidance caps freestanding sandbag walls at 3 ft (5 ft absolute maximum).
Why this beats traditional sandbags
Traditional sandbags require roughly 3× the bag count of StormBags for the same barrier, because each burlap bag is filled two-thirds full and stacked in a pyramid pattern for stability. That means shoveling 30–40 lb of wet sand per bag, transporting it to your property, and stacking it — typically 4–6 person-hours for a single doorway. StormBag ships dry at 1 lb per bag, hydrates in about 3 minutes in fresh water, and stacks in interlocking rows without a pyramid base. For the full comparison, read sandless vs traditional sandbags.
For a deeper walkthrough of the USACE math and worked examples, our companion post how many sandbags do I need to protect my house covers the numbers door-by-door.