I was looking for a bed mattress for camping recently for my Ram 1500 truck, and I realized I didn’t know some basics about my truck. How long is the bed? How do I fit it over the wheel wells? What width do I need?

Bed mats, and a million other truck accessories like a tonneau covers, camper shells, tool boxes, carriers, rails and more come in a variety of sizes, in fact more than I ever could have imagined, so I had to get accurate measurements.

What are the truck bed basics?

First, grab a good, long, tape measure. I know it sounds basic, but many home tape measures only got to three feet. You’ll need one that’s at least seven feet. It’s also important to know the parts of a truck bed. First, you have the bulkhead, which is the part of the bed nearest the cab. Then you have the tail gate. Then you have the sides, and the wheel wells which have varying widths.  

Knowing the best way to measure your truck bed can also help you plan a custom interior, like this example from camber shell manufacturer Leer, a company that makes custom truck caps and tonneau covers. Remember, not every truck has a standard truck bed.

What’s the best way to find the length of your bed?

Many videos will show measuring from the inside bulkhead to the top of the tailgate. This method is close, but it’s not really the best because it doesn’t measure the entire length. Instead, the best way is to put the tail gate down and put one end of your tape measure on the bulkhead and go all the way to the end of the bed where it meets the tail gate. With this method, you then know the proper length, however you’ll have to account for any bed liner width. With the tailgate down, you can also find out how long your gate is in case you have to carry something longer like a motorcycle or lumber.

Also, many small trucks like the Nissan Frontier, may not have the room for a toolbox between the bulkhead and the wheel wells, so for some accessories, you may want to measure that distance, as well.

Measuring your truck bed width can be a bit more complicated

Measuring the width of the bed depends on your truck. Some trucks, like a Toyota Tacoma, have very shallow wheel wells. Others, like dual axle trucks, have giant wheel wells. Simply measure the distance between those wells because many accessories, like a mattress, won’t fit flat if you don’t have enough room. And, just so you know, a sheet of plywood is 4 feet by 8 feet, and not every truck bad can fit one, while others like Rivian’s R1T truck have created interesting ways to fit large objects.

Measuring the width of the inside is a bit trickier, however, because the bed bows out beneath the rails on the top of the bed. Some trucks have Ram Boxes, and flare-side trucks have different widths, too. Typically, all you need is the length for a tonneau cover or other accessories, but that’s not always the case.

The difference between the ultimate inside width and the top rails is different. For a camper shell, for example, you may need to know the measurements on the top of the rails (though not always). For toolboxes and mattresses, you’ll need to know the inside width as well. Some trucks have rails on the inside, too, for tie-downs, so pay attention to how far they stick out.

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