Sandbag Calculator
A 50 ft sandbag wall 2 ft high needs about 1,000 bags (1,100 with 10% extra) and 16.3 yd³ of sand. Base width is 3 × height. Enter length and height.
How many sandbags do I need?
A sandbag calculator turns wall length and height into a bag count. A 50 ft wall that is 2 ft high needs about 1,000 bags. With 10% extra for waste, that is 1,100 bags, 16.3 cubic yards of sand, and about 22 tons.
Enter the length and height of the barrier. The calculator returns the bag count, the base width, the sand to order in cubic yards and tons, and the weight of one filled bag. Add your bag and sand prices to get a cost.
The pyramid rule
Sandbags are not stacked like a straight brick wall. A barrier that holds back water is built as a pyramid, wide at the bottom and narrow at the top.
The U.S. Army Corps of Engineers rule of thumb is base width = 3 × height. A 2 ft high barrier is 6 ft wide at the base. A 3 ft barrier is 9 ft wide.
That is why the count climbs faster than the height does. Doubling the height from 1 ft to 2 ft more than doubles the bags, from 800 to 2,000 per 100 ft. Tripling it to 3 ft needs 3,400. The extra width is what stops the wall from sliding or tipping under water pressure.
Short walls of four bags high or less can be a simple vertical stack backed by clusters of bags. For water deeper than about 2 ft, build the pyramid.
Where the numbers come from
The calculator uses the bag counts published by the U.S. Army Corps of Engineers, St. Paul District, for 100 feet of dike:
- 1 ft high: 800 bags
- 2 ft high: 2,000 bags
- 3 ft high: 3,400 bags
A second self-help flood guide gives the same 2,000 and 3,400 figures, plus about 10,000 bags for 6 ft. For 1 ft it gives a range of 600 to 800 bags. We use the higher figure.
Heights between those points are interpolated in a straight line. Anything taller than 6 ft extends the last slope. Treat heights above 3 ft as rough, because real walls that tall are engineered.
Sources disagree on some details, so here is what we picked. The bag is the common 14 × 26 in size, filled half to two-thirds full. USACE puts a bag at about 30 lb and notes people carry about 40 lb. We use 0.4 cubic feet and 40 lb, which sits in the middle of the published sand totals. Sand is converted to tons at 1.35 tons per cubic yard, the same figure as our sand calculator.
Bags needed by height
| Wall height | Base width | Bags per 10 ft | Bags per 100 ft |
|---|---|---|---|
| 1 ft | 3 ft | 80 | 800 |
| 2 ft | 6 ft | 200 | 2,000 |
| 3 ft | 9 ft | 340 | 3,400 |
| 4 ft | 12 ft | 560 | 5,600 |
These counts have no waste added. The 4 ft row goes beyond the published table and is extended from the same slope. Walls that tall need professional guidance.
How much sand per bag
At 0.4 ft³ per bag, the sand adds up like this:
| Bags | Sand (ft³) | Sand (yd³) | Sand (tons) |
|---|---|---|---|
| 1 | 0.4 | 0.015 | 0.02 |
| 100 | 40 | 1.48 | 2.0 |
| 1,000 | 400 | 14.81 | 20.0 |
One filled bag weighs 40 lb. One ton of sand fills about 50 bags, and a 10 cubic yard load fills about 675.
Worked examples
- Garage door barrier: 50 ft long, 2 ft high (the default)
- Bags per foot at 2 ft: 20
- Bags: 20 × 50 = 1,000
- With 10% extra: 1,100 bags
- Sand: 1,100 × 0.4 = 440 ft³, or 16.30 yd³
- Weight: 1,100 × 40 lb = 44,000 lb, or 22.0 tons
- Cost at $0.75 a bag and $40 a ton: $825 + $880 = $1,705
- Low diverter: 30 ft long, 1 ft high
- Bags per foot at 1 ft: 8
- Bags: 8 × 30 = 240
- With 10% extra: 264 bags
- Sand: 264 × 0.4 = 105.6 ft³, or 3.91 yd³ (5.3 tons)
- Cost: $198 + $211 = $409
- Short tall wall: 20 ft long, 3 ft high, 9 ft base
- Bags per foot at 3 ft: 34
- Bags: 34 × 20 = 680
- With 10% extra: 748 bags
- Sand: 748 × 0.4 = 299.2 ft³, or 11.08 yd³ (15.0 tons)
- Cost: $561 + $598 = $1,159
Filling and laying tips
- Fill half to two-thirds full. A flat bag stacks tight. A fat bag leaves gaps.
- Work in pairs. One person holds the bag open and the other shovels. Wear gloves and eye protection.
- Use sand if you can. Silt and clay are hard to pour and shape. Gravel does not shape well.
- Do not tie the bags. Fold the open end under the bag so the next bag presses it shut.
- Clear the ground first. Strip sod and debris. Dig a shallow key trench a bag deep and two bags wide if you can.
- Lay bags like bricks. Stagger the seams on every layer. Alternate lengthwise and crosswise layers.
- Tamp each bag flat. Finish a layer before starting the next.
- Keep the fold of the bag facing away from the water. The closed bottom should face upstream.
- Leave working room. Keep the wall 6 to 8 ft clear of a building so you can pump out seepage. Do not build directly against a wall.
- Add plastic. A loose sheet of 6 mil plastic on the water side cuts seepage. Do not pull it tight, or the water pressure tears it.
Safety and limits
Sandbag barriers are temporary. They slow and divert water but do not make a watertight seal, and bags that have sat in floodwater are contaminated. Filled bags also rot quickly if left out.
Each filled bag weighs 30 to 40 lb. Lift with your legs, use team carries, and take breaks.
Do not use sandbags as the only protection against wave action or fast current. Follow local emergency management guidance. Many towns hand out free sand and bags before a flood and can tell you the height to build to.
Need to buy the sand? Run the volume through the sand calculator or price it with the sand cost calculator.
This is a planning estimate based on published flood-fight guidance. It is not an engineering design. Check conditions with your local emergency management office.
Frequently asked questions
How many sandbags do I need for a 10 ft wall?
It depends on height. Following the U.S. Army Corps of Engineers table, a 10 ft stretch needs about 80 bags at 1 ft high, 200 at 2 ft, and 340 at 3 ft. Add roughly 10 percent for torn bags, corners, and ends. Height drives the count fast because the base must be three times as wide.
How much sand fills one sandbag?
A standard 14 × 26 in bag filled half to two-thirds full holds about 0.3 to 0.4 cubic feet of sand, or 30 to 40 lb. This calculator uses 0.4 ft³ (about 40 lb) per bag. At that size, 100 bags take 40 ft³, which is 1.48 yd³ or 2.0 tons.
Why are sandbags only filled half full?
A half to two-thirds full bag is flat and flexible, so it molds to the bag below it and the gaps close. An overfilled bag is round and stiff, leaves channels for water, and is too heavy to lift safely. Untied bags with the open end folded under are the standard recommendation.
How tall can a sandbag wall safely be?
Guidance from flood-fighting agencies is to keep walls at about 3 ft or lower. The count climbs steeply as height rises: 100 ft of dike takes about 2,000 bags at 2 ft but 3,400 at 3 ft, and around 10,000 at 6 ft. Above 3 ft, ask your local emergency management office about better options.
Do sandbags stop a flood completely?
No. Sandbags slow and divert water but they do not make a watertight seal. They are a temporary measure, and the sand and bags are ruined by floodwater. Follow local emergency management instructions, and consider plastic sheeting on the water side to cut seepage.
Estimates only. Verify quantities with your supplier before purchasing.