Sandbag Flood Protection Guide: Filling, Placing & Limits

Q: How many sandbags do I need?

For a pyramid barrier, the U.S. Army Corps of Engineers table gives about 600, 2,100, 4,500, 7,800 bags per 100 ft at 1, 2, 3 and 4 ft high. A 20 ft barrier 2 ft high takes about 420 bags. Height matters far more than length.

Q: Which bags should I buy?

Woven polypropylene is now the most common sandbag. Burlap bags rot with months of wetting and drying, so filled bags placed too early may not hold up when you need them. Store empty bags dry and out of the sun. Sand is the best fill; silt, clay or gravel work only in emergencies.

Q: How do I fill and carry them without getting hurt?

Wear gloves, eye protection and a dust mask when filling, and lift with your legs, bending at the knees. Floodwater can carry sewage and chemicals: if you can’t avoid it, wear rubber boots, rubber gloves and goggles.

The short version

Check with your town’s emergency-management office first: many hand out free bags and sand during flood warnings.
Sandbags slow and redirect shallow water. They don’t seal it out.
Keep barriers low. The Corps of Engineers’ preferred limit is 3 ft; single stacks only to about 1 ft.
Never walk or drive through floodwater, and leave when you’re told to evacuate.

How many bags and how much sand

Sandbag quantities come from a standard table rather than a formula you work out on site. Height drives almost everything: a taller wall needs more layers and a wider base under every layer.

How many sandbags do I need?

For a pyramid barrier, the U.S. Army Corps of Engineers gives the number of bags per 100 linear feet¹²:

Sandbags per 100 linear feet of pyramid barrier, by height
Height	Bags per 100 ft	Base width, about
1 ft	600	2.5 ft
2 ft	2,100	5 ft
3 ft	4,500	7.5 ft
4 ft	7,800	10 ft

Sandbags for common barrier lengths, before extra bags
Length	Single stack, about 1 ft	1 ft pyramid	2 ft pyramid	3 ft pyramid
10 ft	30	60	210	450
20 ft	60	120	420	900
50 ft	150	300	1,050	2,250

Bags before extra; add some for losses and bracing (the calculator starts at 10%). A single stack is only for low barriers in still water.¹

So a 20 ft barrier 2 ft high takes about 420 bags. Doubling the height from 1 ft to 2 ft takes 3.5 times the bags. The base widths come from the table’s own geometry (three bags across is about 2½ ft); the Corps’ flood-fight manuals also give a rule of thumb of a base about three times the height, so leave room for that footprint³.

How much sand does that take?

Bags are typically about 14 × 24 inches and filled one-half to two-thirds full²; NDSU Extension suggests keeping filled bags to 35 to 40 pounds for handling⁴. At 40 lb a bag, 420 bags hold about 8.4 tons of sand. Confirm with your supplier, since sand weight varies with moisture.

Enter your barrier’s length and height to see the bags, sand and a drawing of the wall.

Sandbag Calculator

Getting bags and sand

Where can I get free sandbags?

Start with your town or county. Many give out empty bags and sand during flood warnings, usually at self-fill sites where you bring your own shovel¹⁴⁴. Supplies are often limited: one county caps them at 10 to 25 bags per person, while supplies last¹⁵. Pick them up before the storm, not during it. Hardware stores and landscape suppliers also sell bags and sand, but stock runs short when a flood is forecast.

Which bags should I buy?

Woven polypropylene is now the most common sandbag⁴. Burlap bags rot with months of wetting and drying, so filled bags placed too early may not hold up when you need them¹⁶. Store empty bags dry and out of the sun⁶. Sand is the best fill; silt, clay or gravel work only in emergencies².

Filling bags safely

How full should a sandbag be?

About one-half to two-thirds full, and leave the bag untied unless it’s going to be moved²⁴. Filling is easiest with two people: one holds the bag open, the other shovels⁴.

How do I fill and carry them without getting hurt?

Wear gloves, eye protection and a dust mask when filling⁶, and lift with your legs, bending at the knees⁵. Floodwater can carry sewage and chemicals: if you can’t avoid it, wear rubber boots, rubber gloves and goggles⁸.

Placing a sandbag barrier

How do I stack sandbags?

Clear the ground, fill low spots first, and lay the bags lengthwise and parallel to the flow of water. Offset each row or layer by half a bag, like brickwork, and walk on each bag to press it into place¹⁴. A single row of bags is generally only for about 1 ft (three layers) of still water; for anything taller, build a pyramid with as many bags across the bottom as there are layers²¹.

Should the barrier go against the house?

NDSU Extension says not to build a dike against a building wall, because of the force it can put on the wall, and to leave at least 8 ft of working room to watch for and pump seepage⁴. That advice is for dikes; low single stacks across doorways are a different, local practice, covered next.

How many sandbags do I need for a doorway or garage door?

A low barrier across a door doesn’t need a pyramid: NDSU Extension says the pyramid shape isn’t necessary at 1 ft or less⁴, and the Corps of Engineers advises keeping single stacks to about three layers, roughly 1 ft². LA County Fire limits a single stack to two layers unless a building backs it¹⁶. The St. Paul District gives 300 bags per 100 ft for a single-width course 1 ft high, about 3 bags per foot¹:

Sandbags for a single stack about 1 ft high across common door widths
Opening	Bags, about 1 ft high	With 10% extra
Entry door, 3 ft	9	10
Double or sliding door, 6 ft	18	20
Single garage door, 9 ft	27	30
Double garage door, 16 ft	48	53

Brace the stack with clusters of bags every 5 ft so it doesn’t tip⁴, and follow your local emergency-management office’s instructions for sealing doors. For your own opening, use the Sandbag Calculator’s single-stack option.

Do I need plastic sheeting?

It can help. The Corps describes sealing a finished barrier with 6-mil polyethylene on the water side³. Don’t lay the bags on top of plastic: NDSU warns that makes the dike more likely to slide⁴.

What sandbags can’t do

Will sandbags keep water out?

Not completely. Sandbags don’t guarantee a watertight seal¹; they slow and redirect shallow water¹⁶, and seepage through them needs pumping⁴. Barriers can also fail if they’re built wrong, aren’t maintained or face more water than expected³.

Will sandbags protect my basement?

Not from water in the ground. Saturated soil pushes on basement walls, and water inside the basement helps brace them, so a flooded basement should be pumped out in stages once the water outside has gone down¹¹. Sewer water backing up through drains is a separate problem that a backflow valve solves¹³.

When should I stop sandbagging?

When you’re told to evacuate: leave immediately¹⁰. Never walk or drive through floodwater, including to fetch or place sandbags. Six inches of fast-moving water can knock over an adult⁹.

After the flood

What do I do with sandbags after a flood?

Treat bags that touched floodwater as contaminated, wear gloves to handle them and wash afterwards. Keep the sand out of sandboxes, playgrounds and waterways⁷⁴. Bags that touched fuel, oil or chemicals go to a permitted waste facility; your local health or solid-waste office says how⁶.

Longer-term protection

What else protects a home from flooding?

Flood insurance, for one: National Flood Insurance Program policies usually take 30 days to start, so buy well before a storm¹². FEMA also recommends sewer backflow valves, and flood vents that relieve water pressure on walls; reusable barriers such as flood gates and inflatable floodwalls are another option¹³. CalcBrite doesn’t recommend a product or installer.

Planning a temporary barrier? Work out the bags and sand before you go.