How to stack 25 kg bags: layer pattern, height and NOM-036

“Sacos no rígidos (como bultos de arena o cemento),” or non-rigid sacks, such as bags of sand or cement. That is how the bag, the bulto or costal of a Mexican plant floor, appears in Appendix I of NOM-036-1-STPS-2018, Mexico’s federal standard on manual handling from the labor ministry (STPS), in the poor-grip column: red level, value 2. When someone asks how to stack 25 kg bags, the standard has already graded part of the answer before anyone measures the line. We start there because the stacking pattern gets solved in an afternoon, and the number of bags that pass over one person’s back gets expensive.

How much weight does NOM-036 allow a worker to lift?

Values from Table 1, section 8.3(b)(2) of the standard (DOF, Mexico’s official gazette, November 23, 2018). The DOF table merges cells, and for that reason we cross-checked our reading with the copy from Mexico’s Ministry of Economy and with the technical guide from IMSS, the federal social security institute. If palletizing, stacking and pelletizing get mixed up in your plant, here is the difference.

Three notes change how you read it. For people over 45, the mass is determined through a medical fitness evaluation, and with a doctor’s approval it can reach the limit of the 18 to 45 group. During pregnancy and for the 10 weeks after childbirth, the standard prohibits loads over 10 kg. And the standard applies from 3 kg in any workplace where manual handling happens more than once a day (sections 2 and 2.1).

The standard took effect on January 2, 2020, and Table 1 has been binding since March 31, 2024, under the agreement published in the DOF on September 23, 2022. Without a doctor’s approval, only one group can lift a 25 kg bag: men aged 18 to 45. That limit also works as a ceiling: the allowed mass gets adjusted downward for frequency, distance, load position, grip and cumulative mass. The NOM-036 guide explains it in full.

What does 10,000 kg per workday mean in bags?

Section 8.3(b)(5) sets two cumulative mass limits: 10,000 kg per 8-hour workday for distances under 10 m, and 6,000 kg over a distance of no more than 20 m. The standard writes them per workday; we read them per person, which is the cautious reading. Converted to bags, in a Target Robotics calculation:

A line running 4 bags of 25 kg per minute puts out 1,920 bags and 48,000 kg in 8 hours. Divided by 10,000 kg, that volume takes at least 5 people from this limit alone. At one bag every 14 seconds, a person reaches the 400 bags in 93 minutes.

With 50 kg bags the math settles itself. The rule in section 8.3(b)(3) gives a two-person team two thirds of the sum of their capacities, 33.3 kg with men aged 18 to 45, and a three-person team half, 37.5 kg. Neither is enough. That leaves auxiliary equipment, machinery or splitting the load.

How to stack 25 kg bags on a pallet, step by step

1. Check the pallet. The CPC 40 cement data sheet from GCC, a Mexican manufacturer, asks you to remove nails and avoid broken boards that could damage the bags.
2. Measure the filled bag. The math below assumes 60 x 40 x 12 cm; that is our assumption, and your own measurement overrides it.
3. Build the layer of 5. Three bags with their 40 cm side along the 1.20 m side take up 60 cm of depth; two with their 60 cm side take up the remaining 40 cm.
4. Turn the next layer 180 degrees. The two land on the three and the joints cross. The World Food Programme guide (2022) asks for the same number of units per layer, in an interlocking pattern.
5. Keep the bags flat and flush with the edge. The Paper Sack Manufacturers’ Association considers interlocking flush with the pallet the most satisfactory method, and if overhang is unavoidable, it should stay within one inch.
6. Secure the load. GCC recommends bands or straps, with protection on the friction surfaces if rope is used.

The bag size changes how many bags fit per layer. Target Robotics calculation with an exhaustive search of layouts:

A few extra centimeters on the bag can cost two bags per layer. The math is strict and a bag gives a little when squeezed, so it is worth testing with an actual layer built on the pallet. With 5 per layer, 8 layers give 40 bags, 1,000 kg and 1.11 m including a 15 cm pallet; 10 layers give 50 bags, 1,250 kg and 1.35 m. Check that weight against the capacity of your pallet and your rack.

How high can you stack bags?

We found no number in the Mexican standard. NOM-006-STPS-2023 (DOF, March 7, 2024, in force after 180 days), the labor ministry’s standard on storing and handling materials, requires setting the maximum height based on the mechanical strength, shape and dimensions of materials and packaging, and on how they are placed (section 9.4(b)). It also requires marking that height, placing the heaviest material at the bottom, unstacking from the top and keeping materials from leaning on walls. Its scope speaks of storing and handling materials with machinery, although its definition of storage includes placing them by hand; if a forklift moves your pallets, treat it as applying to you and confirm with your safety team. Each plant has to write its own maximum height, with its procedure and its packaging.

As an outside reference, the World Food Programme guide (2022) sets 2.5 m for sacks heavy enough to injure someone, and 3:1 between height and base. Spain’s INSST, the national occupational safety institute, agrees on 3:1 for unsupported stacks and allows 4:1 with good friction (NTP 1112, 2018). For cement, GCC asks for orderly stacks with at least 5 cm between them, a dry covered place, using the oldest stock first and avoiding storage beyond 3 months.

What score does a manual stacking job get?

Appendix I of NOM-036 gives a method with colors and points. We ran it on an example job: one person, a 25 kg bag from the belt to the pallet, dry floor with no obstacles. It is a Target Robotics calculation with those assumptions, and the weight row is our reading of the chart in the standard.

The standard’s scale is 0 to 4 low, 5 to 12 medium, 13 to 20 high and 21 to 32 very high. At medium it asks you to examine the task in more detail or implement an ergonomics program; at high, quick action with that program. Our example assumes a moderate posture, and the standard asks you to score the worst case: if the first layer forces someone to bend down to the floor and reach out with the arms, the 14-second example climbs to 18.

In our reading of the chart, 25 kg sits above the green band at every frequency, even with one lift a day, where green ends near 23 kg. With a 25 kg bag, the manual job starts out with points on the board even when the line runs slowly.

When does it make sense to automate bag stacking?

You can pull three signals from your own data: more than 400 bags per person per shift, a job at the high level of Appendix I, and two or three shifts running. The standard recognizes other ways out, such as auxiliary equipment or smaller bags, and on one shift they often make more sense than a robot.

With a US$100,000 cell, payback on labor alone runs 11 to 16 months at 3 shifts with 4 people per shift, 23 to 31 months at 3 shifts with 2 people, and 69 to 93 months at 1 shift with 2 people. It is a Target Robotics calculation with assumptions (November 3, 2026): a cost of MXN 14,000 to MXN 19,000 per person per month, 71% fewer operators as a target (HowToRobot, 2026), and leaving out maintenance, scrap, injuries and turnover. The cost of manual palletizing in Mexico and when a robotic palletizer pays off work through it.

For the technical side there is the bag palletizer robot page, and for your own numbers, the payback calculator with Mexican wages. Either one needs the weight and size of the filled bag, the bags per minute, the shifts and the Appendix I score of the current job.