Sand Bags for Flood Protection: How Many Do You Need?
Flood protection planning guide
Sand bags for flood protection: how many do you need?
Use a simple per-metre estimate to plan your sandbag order, then adjust for wall height, width, fill weight and site conditions.
Planning note: These figures are for procurement planning only. Sandbag barriers are temporary flood-mitigation measures, not a substitute for evacuation advice, flood warnings or a site-specific engineering design.
The quick answer
Start with the length of the barrier
For a low, single-row barrier made with typical 36 cm × 85 cm sandbags, allow approximately 3–4 filled bags per linear metre, per layer.
A two-layer barrier therefore needs around 6–8 bags per linear metre. Add 10–15% extra for corners, overlaps, damaged bags and changes in the line of the barrier.
The simple formula
Length × bags per metre × layers × rows deep
Then add a 10–15% contingency. For taller or wider barriers, calculate each course separately and seek site-specific advice.
Make the estimate quickly
A practical sandbag quantity guide
01 - ONE LAYER
3–4 bags per metre
Use this as a starting point for a single row and single layer of standard 36 cm × 85 cm bags.
02 - TWO LAYERS
6–8 bags per metre
A common low-barrier planning figure where the second course is staggered over the first.
03 - THREE LAYERS
9–12 bags per metre
Use a wider base and confirm the design where the wall is exposed to higher water or flow pressure.
What changes the number
The per-metre figure is only the starting point.
The finished barrier depends on the bag size, fill level, number of courses, number of rows deep and the shape of the site. A corner, doorway or change in ground level can also require extra bags.
Allow for:
- Bag dimensions and how much they flatten when filled
- Two-thirds fill rather than maximum capacity
- Extra courses needed for the expected water level
- A wider base for taller or higher-flow barriers
- Corners, openings, overlaps and uneven ground
- 10–15% spare stock for real site conditions
Bag size and fill weight
Fill for stability, not maximum weight
Pacific Packaging Australia’s standard flood-control sandbags are 36 cm × 85 cm. When filled, they should flatten and interlock rather than remain rigid.
- Fill each bag about two-thirds full.
- Allow roughly 15–20 kg of sand per bag as a practical guide.
- Do not overfill; heavy, rigid bags leave gaps and are harder to place.
- Use clean sand where possible, as soil can turn to mud and wash out.
Actual weight varies with sand type, moisture and compaction. Fill and weigh one sample bag before a large deployment so your team can plan handling and total sand requirements.
Choose the closure around the workflow
Tie-up or open-top: match the bag to the response plan
Tie-string bags can be closed after filling, while open-top bags can be folded, secured or covered as part of the stacking method. Both formats can suit flood control, construction containment and erosion-management work.
Useful where teams want a simple closure before moving and placing bags.
Useful where speed of filling matters and the mouth is folded into the stack.
Test-fill one bag from the chosen product before ordering a large quantity. The filled shape and handling weight matter as much as the empty dimensions.
Build the barrier correctly
Stack like brickwork and keep the wall stable.
1. Plan the line
Protect doorways, roller doors, low windows, drains and other likely entry points first. Keep an exit route open.
2. Lay flat
Press each bag down and flatten the top before adding the next course. Consistent fills make a more stable wall.
3. Stagger joins
Offset the next course like brickwork so seams do not line up and create channels for water.
For taller barriers: Use a wider base and taper upper courses. NSW SES guidance recommends two rows wide when a wall is more than five bags high. Sandbag walls reduce water entry but are not watertight, so plan how water will be removed from the protected side.
Choose the right stock
Sandbags for councils, contractors and emergency response teams.
Frequently asked questions
Common questions before ordering sandbags
Are the sandbags supplied empty or pre-filled?
The sandbags in this range are supplied empty. This makes them easier to store, transport and distribute before they are filled on site.
How should empty sandbags be stored?
Store empty woven polypropylene bags in a cool, dry place away from direct sunlight and moisture. Keep sand dry and covered so it is ready when needed.
Can sandbags be reused after a flood?
Inspect bags before reuse and follow local council or emergency-service advice. Floodwater can contain sewage, chemicals, oils and other contaminants. Wear sturdy gloves and dispose of contaminated material according to local requirements.
Will a sandbag wall stop floodwater completely?
No. Sandbag barriers can reduce the amount of water entering an area, but they are not watertight and can fail if they are too high, too narrow, poorly stacked or overtopped.
How many bags do I need for a longer or taller wall?
Multiply the barrier length by the bags per metre, number of layers and rows deep, then add at least 10–15% spare. For high-flow, high or wide barriers, confirm the design with a qualified flood or civil engineering professional.
Ready to plan your stock?
Browse sandbags for flood protection, construction and site containment.
Compare tie-up, open-top and high-visibility options, or contact the Pacific Packaging Australia team for help with pack sizes and commercial quantities.
Related reading: How to use sandbags to protect your home.