How can I know if a gig is too heavy or over-sized for me to carry?

Only you can know your personal physical limits. Roadie has no way of knowing or judging whether you are physically capable of delivering a Gig that you have offered on. When you offer on a Gig you are agreeing that you have the physical ability to accomplish it.
Although OSHA does not have any standard which sets limits on how much a person may lift or carry, the National Institute for Occupational Safety and Health (NIOSH) has developed a mathematical model that helps predict the risk of injury based on the weight being lifted and other criteria which can be found in the Applications Manual for the Revised NIOSH Lifting Equation: .  The NIOSH document provides only voluntary guidelines.
According to the website, the difficulty with assessing risks associated with lifting is that weight alone does not determine the risk for back injury. Other factors include:
• How often you are lifting something.
• Whether you bend or twist while lifting.
• How high an object is lifted.
• Where the origin of the lift occurs; specifically, whether it is below knuckle height.
• Whether you hold the object away from you while lifting.
• How long you lift or hold the object.
Depending on these factors, an object that is safe to lift at one time can cause back problems another time.
NIOSH has a lifting equation (discussed in the above-referenced Applications Manual) for calculating a recommended weight limit for one person under different conditions. The lifting equation establishes a maximum load of 51 pounds, which is then adjusted to account for how often you are lifting, twisting of your back during lifting, the vertical distance the load is lifted, the distance of the load from your body, the distance you move while lifting the load, and how easy it is to hold onto the load.
The NIOSH mathematical model and lifting equation are fairly technical, and several state agencies have developed tools that may help you more readily determine whether a job puts you at risk for back injury. 
The Ohio Bureau of Workers’ Compensation has a calculator for assessing risk levels associated with lifting various weights, which is available at
Similarly, the Washington State Department of Labor and Industries [and the Oregon State Safety and Health Division have jointly] developed a calculator for analyzing lifting tasks, based on the NIOSH lifting equation, which is available at
Remember, you are responsible for knowing your own physical limitations.
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