Earthbag House Calculator
Estimate bag count, soil volume, and barbed-wire length for an earthbag wall from wall geometry and tamped bag dimensions.
Tamped bag dimensions
How this works
Earthbag walls are built up in courses, with two strands of barbed wire between courses for tensile bond. Bag count comes from a simple stacking calculation:
courses = ceil(wallHeight / bagHeight)
bagsPerCourse = ceil(wallLength / bagLength)
bagCount = courses × bagsPerCourse
soilVol = bagCount × bagW × bagH × bagL × 0.95 (5% void)
barbedWire = 2 × wallLength × coursesThe 5% void allows for compaction and air pockets inside the tamped bag.
Worked example
A wall 30 m × 2.4 m, bags 0.40 × 0.10 × 0.55 m:
- Courses = ceil(2.4 / 0.10) = 24
- Bags per course = ceil(30 / 0.55) = 55
- Total bags = 24 × 55 = 1,320
- Soil = 1,320 × 0.022 × 0.95 ≈ 27.6 m³
- Barbed wire = 2 × 30 × 24 = 1,440 m
Sources
- Cal-Earth / Hunter & Kiffmeyer earthbag practice (course stacking, 2 strands of barbed wire per course)
FAQ
What is an earthbag wall?
An earthbag wall is built by filling polypropylene sandbags or continuous tubing with damp subsoil, laying the filled bags in courses like masonry, and tamping each course flat before adding the next. Two strands of barbed wire between every course act like reinforcing — they grip both bags and prevent the wall from sliding under lateral load. The technique was developed by architect Nader Khalili at Cal-Earth.
What soil works best for earthbag fill?
A subsoil with 10 to 25 percent clay and 70 to 85 percent sand or gravel performs best. Pure sand has no cohesion. Pure clay shrinks and cracks. The fill should hold a clear fingerprint when squeezed but break apart when poked. Test a small batch by filling and tamping a single bag; if it stays dense and stiff after 24 hours, the soil is good.
Why two strands of barbed wire per course?
Two parallel strands of 4-point barbed wire run between each pair of courses. The barbs grip the polypropylene fabric and lock the bags in place, giving the wall tensile capacity along the horizontal joint. Without the wire the wall would slip under wind, seismic, or arch-thrust loads. Use galvanised wire to avoid rust through the long life of the wall.
Why is a 5 percent void deducted from the soil volume?
Even after thorough tamping, every bag retains some air pockets and a small unfilled volume at the seams. Deducting 5 percent from the geometric bag volume gives a more realistic order quantity for the soil. If you are using larger bags or working in dry / dusty conditions, the void may be slightly higher (7 to 10 percent).
Are earthbag walls safe in earthquakes?
Earthbag walls have performed well in shake-table tests up to seismic intensity comparable to Nepal's 2015 Gorkha quake, but only when properly detailed: continuous barbed-wire courses, vertical buttressing or curved walls, a strong ring beam at the top, and a roof that does not load the walls eccentrically. Plain earthbag walls without these features are not earthquake-safe. Always involve a structural engineer for a habitable structure in seismic zones.
Do I need to plaster the bags?
Yes — polypropylene fabric degrades in UV in 1 to 2 years if left exposed. The standard finish is a thick lime or cement-stabilised earth plaster, applied in 2 or 3 coats over a chicken-wire reinforcement layer. The plaster also protects against rodents and erosion. Internal walls can use a thinner mud or lime plaster.