Manual Handling Calculator: NIOSH Lifting Equation and Lifting Index

The recommended weight limit for a lift and the lifting index of the load you really lift, to help rank manual handling tasks.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Whether a lift is risky does not depend on weight alone. It depends on how far from the body the load is held, how high it starts, how far it travels, how much the body twists, how often it is lifted and how good the grip is. The NIOSH lifting equation turns each of these into a multiplier below 1 and applies them to a 23 kg load constant.

The result is the recommended weight limit for that lift. Dividing the actual load by it gives the lifting index: at or below 1 the lift is within the recommended limit, above 1 it is over, and 3 or more is high risk for many workers.

The equation covers smooth two-handed lifts in front of the body in good conditions only. There is no legal weight limit for lifting: the duty is to eliminate or reduce the risk of the manual task, by changing the task, the layout, the load or the equipment.

Formulas used

  • RWL = 23\,HM\,VM\,DM\,AM\,FM\,CM
  • HM = 25/H
  • VM = 1 - 0.003\,|V-75|
  • DM = 0.82 + 4.5/D
  • AM = 1 - 0.0032\,A
  • LI = \text{load}/RWL

Worked example

With the default numbers in the calculator above:

  1. Horizontal multiplier: 0.83
  2. Vertical multiplier: 1.00
  3. Distance multiplier: 1.00
  4. Asymmetry multiplier: 1.00
  5. Frequency and coupling multipliers: 1.00 and 1.00
  6. Recommended weight limit: 19.17 kg
  7. Lifting index: 0.78

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: Horizontal distance of the hands from the body (between the ankles) 40 cm; Height of the hands above the floor at the start of the lift 50 cm; Vertical distance the load travels 60 cm; Angle the body is twisted (asymmetry) 30 deg.

  1. Horizontal multiplier: 0.63
  2. Vertical multiplier: 0.93
  3. Distance multiplier: 0.90
  4. Asymmetry multiplier: 0.90
  5. Frequency and coupling multipliers: 1.00 and 1.00
  6. Recommended weight limit: 10.76 kg
  7. Lifting index: 1.39

Common questions

What is a safe weight to lift?

There is no single safe weight. A light load held far from the body, lifted from the floor many times, can be riskier than a heavier load lifted once at waist height. Use the task, not just the weight.

What does a lifting index of 1 mean?

The load equals the recommended weight limit for those conditions. It is a recommended limit designed for most healthy workers, not a guarantee for everyone.

Does it cover pushing, pulling and carrying?

No. The equation is for lifting and lowering only. Other tasks need their own assessment.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Waters, Putz-Anderson, Garg and Fine (1993), Revised NIOSH equation for the design and evaluation of manual lifting tasks; Hazardous manual tasks Code of Practice (Queensland).

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