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Using Reference IDs helps reduce duplicate inputs, keeps values consistent, and allows your calculations to automatically update when inputs change. This is especially important in engineering calculations, where the same value is often used in multiple places. By referencing a single value, you minimize the risk of input errors, avoid mismatched assumptions, and ensure that updates automatically track throughout the calculator. This not only saves time, but also improves accuracy, transparency, and confidence in the results. Anywhere you can type a value, you can use “Reference IDs”, also known as “Formula References” to use already inputted or calculated values. For any of the existing variables within a calculator, you can find the corresponding formula reference by opening the dropdown tab, which is located next to any calculated or inputted value- simply by clicking on the text. Image (2)
All of these values are unit-aware, meaning they’ll automatically handle unit conversions (we’ll also check that units are convertible).
These often differ per calculator, but some common ones are outlined below:

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Common Beam Reference IDs

In these calculators, values from Project Defaults can also be used. For example, typical bearing length is entered as projectDefault("l_b", 3.5). Check out our Project Defaults Cheat Sheet for a more comprehensive list of what can be referenced in your calculators!

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Common Column Reference IDs

You can use any of these values in a formula as well. For example, to place a support in the center of your column you can simply type in “L/2” for simplicity.

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How beam span length (L) is measured

For Calcs.com beam calculators, L refers to the full plan length of the member, measured from the start of the beam to its end, including any intermediate supports. It is not just the clear span between two adjacent supports. This matters most on multi-span beams. If you have a 3-support beam with a 10 ft back span and a 10 ft front span, L is the total 20 ft, not either 10 ft segment on its own. Intermediate supports are then defined by their position along that total length, not by breaking the member into separate spans. Wood beam sheet showing Beam Plan Length set to 20 ft with pinned supports at 0, 10, and 20 ft
If you set L to a single clear-span value on a multi-support beam, you’ll under-report the true length of the member and the calculator will use the wrong geometry for shear, moment, and deflection. Always enter the plan length end to end.
The same convention applies to Column Height (L) in column calculators. It is the total height of the column from start to end, including any intermediate lateral supports (see the Common Column Reference IDs table above).