Derive the laid length, do not measure it
Ask five earthbag builders how long a filled bag is and you get five answers, because the question has no fixed answer. A poly bag is a limp container. Put soil in it, drop it on the course, walk it flat and hit it with a tamper, and it becomes whatever shape the wall is being built to. Its thickness is set by how wide the course is being run, its height is set by how hard it is tamped, and its length is simply whatever is left over once the volume has to fit inside those two.
So the arithmetic runs the other way from the way people usually try it. Take the loose fill volume you actually put in a bag, divide by the loose to tamped ratio to get the volume it becomes in the wall, then divide that by the course cross-section. What comes out is the run one bag covers. On the defaults here — 1.1 cubic feet of loose soil, a ratio of 1.25, a 15 by 5 inch tamped course — one bag ends up lying 1 ft 8-1/4 in along the wall, and that is the number the whole count is built on.
The practical use of this is that it tells you what to change. Bags per course too high? Fill fuller. Wall going up too slowly? Both fill volume and tamped course height are levers, and they pull in different directions on the bag count and on how much soil you have to move.
Loose and tamped are different volumes and only one of them is the wall
Everything you dig, order, wheel and shovel is loose. Everything that ends up standing is tamped. On the defaults a 30 by 6 foot wall with two small openings is 7.22 cubic yards of wall, and the soil you have to move to build it is 10.23 cubic yards — the difference being the loose to tamped ratio and the spare bag allowance. Order on the first number and you come up short a quarter of the way through.
The calculator also prints the wall volume twice, once from the geometry and once from the bag count, and divides one by the other. The bag figure runs a little high because courses and bags per course both round up. If it runs a lot high, the section or the fill volume you entered is not the section or the fill volume you are actually building to, and it is easier to find that out on a page than on the fourth course.
Wire goes between courses, not on them
A small point that changes the order: the joints between courses are one fewer than the courses. Eight courses meet at seven joints. On a long wall with a lot of courses the difference is one run of wall length times the strand count, which is not enormous, but it is the kind of quiet plus-one or minus-one that shows up in every layout problem and is worth getting right rather than guessing.
What is not here
No strand count, no course height rule, no soil specification, no maximum wall height, no view on whether a bag wall of the section you entered does what you need. Earthbag walls sit outside the prescriptive path in most adopted codes. Permitting one usually means an alternative materials review and frequently an engineer stamping the wall, and the section, the reinforcement and the connections come out of that process rather than out of a calculator.
Two things worth naming without dressing them up. An earthen wall that is saturated before it is protected is a different and worse wall than the one that was designed, and rain during the build is a real risk on a job that goes up slowly. And this is a build where the same heavy lift is repeated several hundred times a day at ground level, which is where people actually get hurt on these sites.
Questions people ask
How long is a filled earthbag?
Whatever the fill volume and the tamped section make it, which is why this page derives it. A bag is a limp container that takes the shape of the course, so the length it occupies falls out of the volume divided by the cross-section. On the defaults here that comes to 1 ft 8-1/4 in per bag. Fill the bags fuller or run a thinner course and the number moves, which is why a count taken off another wall will not match yours.
How much soil does an earthbag wall need?
Two answers, and the difference between them matters. The wall itself, tamped, is the net face area times the thickness. The soil you have to dig or buy is that figure multiplied by your loose to tamped ratio, because material is handled loose. On the defaults the wall is 7.22 cubic yards and the soil to dig or buy is 10.23 cubic yards. Order the second number.
How much barbed wire goes between the courses?
The run length times the strand count times the number of joints, and the joints are one fewer than the courses. This page takes the strand count from you because it is a design decision and not a fact about earthbags. Ask whoever is designing or stamping the wall what the pattern is, and this page will count the linear feet and the rolls.
Is this the same as a sandbag flood barrier?
No, and there is a separate page for that. A flood barrier is a stacked triangular profile built quickly from bags whose filled size you already know, and the questions are base width, bag count and how many people-hours the filling takes. This page is a vertical wall built to a tamped section, where the laid length has to be derived and the barbed wire and the loose soil supply are the additional items.
Will an earthbag wall pass inspection?
That is a question for your building department, asked early. Earthbag construction sits outside the prescriptive path in most adopted codes, so the normal route is an alternative materials review, and in many jurisdictions an engineer has to stamp the wall. This page has no requirement of its own, offers no height limit and makes no adequacy judgement. It counts bags, wire and soil for a design somebody qualified has already settled.