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Calculating Recommended Weight Limit (RWL)

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What is the Revised NIOSH lifting equation?

The equation is:

LC x HM x VM x DM x AM x FM x CM = RWL 

where LC is the load constant (23 kg) and other factors in the equation are:

  • HM, the Horizontal Multiplier factor
  • VM, the Vertical Multiplier factor
  • DM, the Distance Multiplier factor
  • FM, the Frequency Multiplier factor
  • AM, the Asymmetric Multiplier factor
  • CM, the Coupling Multiplier factor
  • RWL, the Recommended Weight Limit

For each value, look up the corresponding factor and use this number in the equation. See Assessing Relevant Handling Factors for explanation of terms.

To use the calculator, click on the values for each factor in the left hand column (or you can input your numbers directly into the second equation). Press the "Calculate RWL" button when you have finished selecting all of the values.

Horizontal Multiplier (HM): Horizontal distance (H, in cm) from the midpoint between the ankles to the hands while holding the object.

H = Horizontal Distance (cm) HM Factor
25 or less 1.00 
300.83
40 0.63
50 0.50
60 0.42
 

Vertical Multipler (VM): The vertical distance (V, in cm) of the hands from the ground at the start of the lift.

V = Starting Height (cm) VM Factor
0 0.78
 30   0.87
 50  0.93 
 70   0.99 
 100   0.93 
 150   0.78 
 175  0.70
 >175  0.00
 

Distance Multipler (DM): The vertical distance (D, in cm) that the load travels.

D = Lifting Distance (cm) DM Factor
25 or less 1.00
 40   0.93 
 55   0.90
 100   0.87 
 145  0.85 
 175  0.85
 >175  0.00
 

Asymmetric Multipler (AM): The twisting angle (A) of the body while lifting, measured in degrees.

A = Angle (degrees) AM Factor
90°  0.71 
 60°   0.81
 45°   0.86 
 30°  0.90
 0°  1.00
 

Frequency Multipler (FM): The frequency (F) of lifts and the duration of lifting (in minutes or seconds) over a workshift.

F = Time Between Lifts  FM Factor
Lifting While Standing: OR Lifting While Stooping:
One Hour or Less Over One Hour One Hour or Less Over One Hour
5 min 1.00 0.85 1.00 0.85
1 min  0.94 0.75 0.94 0.75
30 sec 0.91 0.65 0.91 0.65
15 sec 0.84 0.45 0.84 0.45
10 sec0.750.270.750.27
6 sec0.450.130.45-
5 sec0.37 -0.37 -

 

FM = pick a value from (A) and (B).

(A) Time Between Lifts
Lifting While Standing



Lifting While Stooping

 

Coupling Multipler (CM): The quality of grasp (or coupling, C) classified as good, fair or poor and depends on the body position (either standing or stooping).

C = Grasp CM Factor:
Standing Stooping
Good (handles) 1.00 1.00
Fair 1.00 0.95
Poor 0.90 0.90

CM = pick a value from (A) and (B).

(A)

  

 

The revised NIOSH Lifting Equation is: 23 Kg x HM x VM x DM x AM x FM x CM= RWL
23 Kg x x x x x x =

 

or, input values directly in the equation below:
23 Kg x x x x x x =

Where can I get more information about the lifting equation?

More information is available in other OSH Answer documents. Please see the other documents in the NIOSH Lifting Equation series.

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Document last updated on September 17, 2007
Document confirmed current on October 1, 2012

Disclaimer

Although every effort is made to ensure the accuracy, currency and completeness of the information, CCOHS does not guarantee, warrant, represent or undertake that the information provided is correct, accurate or current. CCOHS is not liable for any loss, claim, or demand arising directly or indirectly from any use or reliance upon the information.