“Dolly” covers at least five genuinely different tools, and buying the wrong category is a more expensive mistake than buying a cheap version of the right one. Here is the whole landscape, with the specifications from the products above rather than round numbers.
1. Four-wheel furniture dolly (flat dolly). A low hardwood or steel deck on four swivel casters. The load sits flat and level on top. Typical deck: 18 x 30 in, about 5 in tall — both the WEN and Simpli-Magic pairs are exactly this. The Mytee is 19 x 32 in and 8 in thick with a 1,000 lb working load limit. Sold in pairs because one cannot carry a sofa. Best at: long, heavy, flat-bottomed pieces on level floors. Cannot do: stairs, at all.
2. Two-wheel hand truck (utility dolly). An upright frame with a nose plate that slides under the load, which then tips back onto an axle. Capacities here run 330 lb (KEDSUM upright), 340 lb (Teprovo aluminum folding, 13 lb, folds to 2 in thick), and 500 lb (Olympia upright). Best at: boxes, bins, stacked loads, tight corridors, and stairs with care. Cannot do: anything wide or flat-bottomed it cannot get a plate under.
3. Appliance hand truck. A heavier two-wheel frame with a securing strap and stair glides. The Harper 6781 is 800 lb, roughly 60 in tall. The strap is the defining feature, not the capacity — it is what holds a tall top-heavy load against the frame. Best at: refrigerators, washers, dryers, freezers, safes. Cannot do: low furniture, or justify its storage footprint if you own it for one move.
4. Platform truck / convertible cart. A wheeled deck with a handle so you push upright instead of crouching. The Rubbermaid Triple Trolley is 500 lb on a 32.5 x 20.5 in deck, 5.9 in high, with a three-position folding handle. Convertibles like the Olympia (1,000 lb platform mode) and KEDSUM (600 lb, brakes, base expanding 27 to 48 in) live here too. Best at: repeated trips with boxes, bins and equipment. Cannot do: tuck under a piece the way a flat dolly does.
5. Sliders and lifting straps — not dollies at all, and often the right answer. Felt or rubber pads that go under the feet so a piece slides rather than rolls. X-PROTECTOR’s hardwood set is 16 pieces at 3-1/2 in across (2-3/4 in internal), felt over rubber foam, reusable with no adhesive. Their carpet set is 8 pieces at 4-3/4 in, the larger diameter spreading the load so it does not sink into pile. Lifting straps are the other half: the KEEPER two-person set is two 3 in straps rated to 800 lb with nine length settings; the Ready Lifter is two harnesses plus a 12 ft x 3 in strap rated to 600 lb, fitting chests up to 44 in. Best at: repositioning within a room, and getting a piece up onto a dolly in the first place. Cannot do: transport across a driveway.
The honest summary: most people who think they need a dolly need sliders, and most people who buy one dolly should have bought a pair. For the full kit including blankets and stretch wrap, see our furniture moving tools roundup.