GMC Sierra 3500HD bed dimensions & sizes by year

The GMC Sierra 3500HD has been offered with 4 bed lengths: 6.9 ft (82.2"), 8.2 ft (98.3"), 6.6 ft (78.9") and 8 ft (98"). The exact bed on your truck depends on its model year and cab — choose your year above to see which covers fit.

On the current Sierra 3500HD (2020–present) the bed floor measures about 51 inches between the wheel wells — the narrowest point and the number that decides what lies flat. That is wider than 48 inches, so a 4×8 sheet of plywood or drywall lies flat on the floor. The bed is wider above and behind the arches; measure your own truck before counting on a tight fit.

The current Sierra 3500HD bed measures 82.2" (6.9 ft) and 98.3" (8.2 ft) with the tailgate closed. Dropping the tailgate adds roughly 18 inches of support on a typical pickup, so plan on about 100" and 116" of load floor with it down. Tailgates vary by a couple of inches — measure yours, and strap anything that overhangs.

The current Sierra 3500HD is 231.9–266" long bumper to bumper depending on cab and bed — the shortest cab with the shortest bed at one end, the biggest cab with the longest bed at the other, 81.9" wide without mirrors and 78.2–81" tall. Check the garage fit before you buy — mirrors and off-road trims add width and height.

Measure the inside floor of the bed, from the bulkhead (the wall behind the cab) to the inside of the closed tailgate. Round to the nearest standard size — tonneau covers are sold by bed-length category (e.g. 5.5 ft, 6.5 ft, 8 ft), not the exact inch.

The current Sierra 3500HD (2020–present) comes with 6.9 ft (82.2") on the Double Cab and Crew Cab and 8.2 ft (98.3") on the Regular Cab, Double Cab and Crew Cab. The cab you choose largely decides the bed, so check the cab before ordering a tonneau cover or bed liner.

Not necessarily. Covers are matched to a specific generation and bed length, and both the bed length and the rail design can change between generations. Always match your exact model year and bed size before buying — the year-by-year table below shows where the Sierra 3500HD changed.

Yes — the longest Sierra 3500HD bed on record is 98.3", so a full 4×8 sheet lies flat with the tailgate closed. Width matters too: a 48-inch sheet only lies flat on the floor if the gap between the wheel wells is wider than 48 inches — on mid-size trucks it rides on top of the wheel arches instead.

Across the model's history the beds run from 78.9" to 98.3" — a difference of 19 inches of usable floor. The longer bed hauls more and takes longer sheet goods, the shorter bed is easier to park and turn. They take different tonneau covers, so the bed you have decides which cover part number you order.

Properly equipped, the Sierra 3500HD has been rated up to 36,000 lb across the generations on this page, with a maximum payload of about 7,442 lb. Those are best-case figures for a specific engine, cab and axle combination — your truck's door-jamb sticker and owner's manual are the numbers that count. Run them through the towing and payload calculators to see what's actually left for a trailer once passengers and gear are on board.

The Sierra 3500HD has been offered as Regular Cab, Double Cab, Crew Cab and Extended Cab. Cab choice is what usually decides bed length — a bigger cab on the same wheelbase means a shorter bed, which is why two trucks from the same year can need different covers.

A little, and only at highway speed. Independent testing puts the gain on a typical pickup at roughly 1–2%, which is real but small — on most Sierra 3500HD trucks that's a few dollars a tank, not a payback plan. Buy a cover for the dry, locked, secure bed; treat the mileage as a bonus.