Sandbag Calculator
Turn doorways, bags per row, and rows into bag totals and next row extras.
What it does
Sandbag walls buy inches against rising water when every doorway gets the same stacked rows. Four openings at 8 bags per row over 3 rows need 96 bags, with 24 shielding each door.
The tool above takes openings, bags per row each, and rows high. It returns total bags, bags each opening, and the extra for one more row, so fill sites can stage piles before rain.
This math counts bags only. It does not set wall heights against forecast depths, plastic sheeting behind stacks, or drainage that decides whether walls hold.
Flood guidance frames the same prep: know flood risk, move valuables high, clear drains, and never drive through flood water. Walls supplement evacuation plans, never replace them.
Fill bags half full for stacking. Overfilled bags roll off walls instead of sealing.
How to use
- Count doors and openings taking water.
- Enter bags laying one row across each.
- Enter rows high the wall must reach.
- Read bags each opening first for crews.
- Read total bags for the fill site order.
- Read one more row for rising water plans.
Formula
- openings
- Doors and gaps shielded alike.
- per row
- Bags laying one course across each.
- rows
- Stacked courses high.
Same rows must apply to all openings. Taller water needs more rows rerun here. Stagger joints like brickwork when stacking.
Worked example
Example: 4 openings, 8 per row, 3 rows
Openings 4, bags per row 8, rows 3.
- Each: 8 x 3 = 24 bags each.
- Total: 4 x 24 = 96 bags.
- Next row: 4 x 8 = 32 bags for row 4.
- Tool shows 96 bags, 24 bags each, 32 bags for one more row.
- Crew: two fillers and two stackers per opening.
Reference table
| Rows | Total bags | Each opening |
|---|---|---|
| 2 | 64 bags | 16 bags each |
| 3 | 96 bags | 24 bags each |
| 4 | 128 bags | 32 bags each |
Limits
- Counts only. Depths and flow decide if walls hold.
- Ignores plastic sheeting behind stacks.
- Ignores seepage and drain backup paths.
- Evacuation orders override any wall plan.
Common mistakes
- Filling bags full so they roll off.
- Stacking straight joints that leak through.
- Shielding doors while water enters through drains.
- Ordering exact bags with no spares for tears.
- Driving through water to reach the wall site.
Try it yourself
Quick checks. Answers sit tucked under each question.
2 openings, 10 per row, 2 rows?
40 bags, 20 bags each, 20 for one more row.
6 openings, 6 per row, 4 rows?
144 bags, 24 bags each, 36 for one more row.
1 opening, 12 per row, 5 rows?
60 bags, 60 bags each, 12 for one more row.
Questions
How many sandbags per doorway?
Bags per row times rows. 8 per row over 3 rows is 24 per opening.
How do I stack sandbags?
Half full bags, staggered joints, tamped tight, with plastic behind for seepage.
What about one more row?
Openings times bags per row. 4 openings at 8 need 32 more bags.
Do sandbags stop all flooding?
No. They divert shallow flows but fail against deep or fast water. Evacuate when told.
Should I drive through flood water?
Never. Six inches of moving water can knock you down and a foot can float cars.
What else should I prepare?
Move valuables high, clear drains, gather supplies, and know evacuation routes.