KingSmith sells the WalkingPad X21 as a treadmill that folds "suitcase size in two simple moves". It sits between the flat WalkingPad desk pads and a conventional folding treadmill. This review explains what the published specs mean in practice, where sources disagree, and which buyers the X21 fits. We have not used the X21 ourselves: the review draws on KingSmith's two official sites, retailer and Amazon listings, and independent reviews from Treadmill Review Guru, TreadmillReviews.com and RunToTheFinish. Our KingSmith WalkingPad review covers the whole brand.
Key specs
These figures come from the WalkingPad.com product page unless noted.
| Spec | WalkingPad X21 |
|---|---|
| Model | X21 (WalkingPad.com also shows X212; manuals list TRX21F) |
| Motor | Brushless, 3.75 HP (WalkingPad.com); 1.25 HP (KingSmith.com) |
| Speed | 1 to 7.5 mph |
| Incline | None |
| Max user weight | 240 lb (KingSmith.com: 243 lb) |
| Belt | 47.6 x 18.1 in |
| Unfolded size | 55.8 x 27.9 x 41.4 in |
| Folded size | 39.6 x 27.9 x 8.8 in |
| Weight | 81 lb net, 92 lb shipping |
| Handlebar | Fixed upright bar, not adjustable |
| Speed control | SpeedDial knob or KS Fit app |
| Remote | No |
| App | KS Fit with NFC quick connect; Apple Watch support |
| Cushioning | EVA and PET layers |
| Assembly | Fully assembled |
| Warranty | 1 year, optional extension |
A double-fold treadmill, not an under-desk pad
The X21 shares a brand with the flat WalkingPad C2, Z1 and P1, but it is built for a different job. Those pads lie flat, have no console and are designed to slide under a standing desk. The X21 has a console post that rises about 41 inches from the floor, with the display and SpeedDial knob mounted on the bar. That bar sits where a desk would need to be, so the X21 is a poor desk walker.
What you get instead is storage. The deck folds in half, then the console folds down against it, leaving a slab 39.6 inches long, 27.9 inches wide and 8.8 inches thick. KingSmith says a reinforced locking mechanism holds the deck shut when folded. The unit rolls on wheels and can stand in a closet or slide under a high bed.
KingSmith explains the lack of incline plainly on the X21 page: an incline would interfere with the fold. That trade-off defines the model.
What the X21's numbers mean at home
Speed in pace terms
The X21's range runs from 1 mph, a slow stroll, to 7.5 mph, which works out to an 8-minute mile. A brisk walk sits around 3 to 4 mph, a comfortable jog for many adults around 5 to 6 mph. So the X21 covers walking and easy running with some headroom, but a runner who trains faster than 8-minute miles will hit the ceiling. RunToTheFinish made the same point, saying the X21 is not built for workouts at around an 8:30 pace or faster. For the general question of running on compact machines, see can you run on a walking pad.
Floor space in use and in storage
Unfolded, KingSmith's figures give a footprint of 55.8 by 27.9 inches, about 10.8 square feet, and you should keep clear floor behind the deck in case you step off the back. Folded, it drops to 39.6 by 27.9 inches and 8.8 inches thick, which is closer to a large suitcase than a treadmill. Measure the gap under your bed or sofa, and the width of any closet door, before you order. Because the folded unit still weighs about 81 lb, plan to roll it on hard floors; if it will live on carpet, read our guide to using a walking pad on carpet.
The console and app
KingSmith describes a dial display on the console that shows your session metrics, with speed set by turning the SpeedDial knob. TreadmillReviews.com lists time, speed, distance, calories and steps on screen. The KS Fit app can also set speed and keeps a record of each session. There are no preset programs on the machine itself, so structured workouts mean changing speed by hand.
Who it suits
- Apartment dwellers who have no spare room for a full treadmill and want it gone when guests arrive. Treadmill Review Guru and RunToTheFinish both named small-space living as the X21's best fit.
- Walkers who jog sometimes. The 7.5 mph top speed is a steady jog for most adults, well above the 4 mph cap on typical walking pads.
- People who like something to hold. The upright bar gives a reference point in front of you, although reviewers note it is not a full safety rail.
- Quiet households. RunToTheFinish and TreadmillReviews.com both described the brushless motor as very quiet. See our guide on walking pad noise for how to cut vibration further.
What stands out
- The fold. Few treadmills that reach 7.5 mph pack down to under 9 inches thick. KingSmith calls it suitcase size.
- Arrives assembled. Both KingSmith sites list the X21 as fully assembled. There are no uprights to bolt on.
- Simple speed control. You turn the SpeedDial knob on the bar to change speed. Treadmill Review Guru's Sydney Kaiser and RunToTheFinish's Amanda Brooks both singled out the dial as easy to use.
- App pairing by NFC. KingSmith lists NFC quick connection to the KS Fit app (KingSmith.com says NFC pairing works on Android). The app logs sessions and links with Apple Watch.
- Wider belt than its rail-equipped sibling. At 18.1 inches, the belt is wider than the 17 inches or so on the Denise Austin model, which gives more room for side-to-side drift at a jog.
Pros
- Folds twice to 8.8 inches thick
- Reaches 7.5 mph for jogging
- Ships fully assembled
- Quiet brushless motor according to independent reviewers
- Simple dial speed control
Cons
- No incline
- 240 lb limit
- About 47.6 inches of belt is short for running
- Fold seam felt underfoot, according to reviewers
- Small wheels struggle on carpet
Drawbacks
- The seam. Sydney Kaiser at Treadmill Review Guru, who reported using the X21 for about two years, described the fold hinge as "a slight bump or dent" underfoot. RunToTheFinish noticed the split at higher speeds, and TreadmillReviews.com also mentioned it.
- Short stride room. All three independent reviews said the belt length restricts taller runners. RunToTheFinish added that the top speed is uncomfortable for sustained efforts.
- Handlebar is not a safety rail. TreadmillReviews.com wrote that the rails "serve more as a reminder of your positioning" than as real support, and that the device rack is unsteady while running.
- Wheels. Treadmill Review Guru found the small transport wheels hard to roll on carpet.
- No remote and no programs. Speed changes happen at the dial or in the app. TreadmillReviews.com noted no built-in training modes.
- Weight to lift. At about 81 lb, it rolls well on hard floors but is heavy to carry upstairs.
Where the numbers disagree
We compared WalkingPad.com, KingSmith.com, three Amazon listing titles and three independent reviews. They disagree on several figures:
- Motor. WalkingPad.com says 3.75 HP. KingSmith.com says 1.25 HP. Treadmill Review Guru lists 1.0 HP, and one Amazon listing title says 918 W. Neither KingSmith page says whether its figure is peak or continuous output, so treat the motor rating as unclear.
- Top speed. KingSmith lists 7.5 mph. Treadmill Review Guru and TreadmillReviews.com list 7.45 mph, and one Amazon listing title says 0.3 to 7.4 mph. The WalkingPad.com FAQ says X Series models reach 11.5 mph, which contradicts the X21 product page.
- Weight limit. WalkingPad.com says 240 lb, KingSmith.com says 243 lb, and an Amazon listing title says 242 lb. We use the lower 240 lb.
- Belt. WalkingPad.com says 47.6 by 18.1 inches; KingSmith.com says 47 by 18 inches; TreadmillReviews.com says 18 by 48 inches.
- Machine weight. KingSmith gives 81 to 82 lb net and 92 lb shipped. TreadmillReviews.com lists 93 lb, and RunToTheFinish says about 90 lb, which may be the boxed weight.
Who should skip it
Skip the X21 if you want to walk while typing: a flat pad from our best under-desk treadmills list suits that job. Skip it if you weigh over 240 lb (the X25 is rated for 300 lb), if you are tall and want to run (see the best walking pads for tall people), or if you want incline training.
How it compares
WalkingPad X25. The X25 is the X21's bigger sibling. KingSmith lists 10 mph, a 300 lb limit and a 51.9 by 19.6 inch running area, about 4 inches longer and 1.5 inches wider than the X21. The cost is weight (104 lb against 81 lb) and a thicker fold (10.1 inches). Pick the X21 if storage and lifting come first; pick the X25 if you are heavier or run more.
WalkingPad Denise Austin 2.0. The Denise Austin model matches the X21 on speed and weight limit but adds side handrails that fold away. Its belt is about an inch narrower. It suits walkers who want support on both sides.
WalkingPad R1 Pro. The R1 Pro folds once rather than twice, weighs 73 lb per KingSmith, tops out at 6.2 mph in running mode and includes a remote. Its handrail retracts, so it can double as a desk pad. Choose it if desk walking matters as much as jogging.
Scroll sideways for all specs →
| Product | Speed | Max user | Belt | Weight | Size | Handle | Remote | Where to buy |
|---|---|---|---|---|---|---|---|---|
1 WalkingPad X21Most compact fold | 1 to 7.5 mph | 240 lb | 47.6 x 18.1 | 81 lb | 55.8 x 27.9 x 41.4 in; folded 39.6 x 27.9 x 8.8 in | ✓ Yesfixed upright bar | ✕ NoNo | Check price on Amazon |
2 WalkingPad X25More speed and capacity | 1 to 10 mph | 300 lb | 51.9 x 19.6 | 104 lb | 60.8 x 30.4 x 40.3 in; folded 10.1 x 30.4 x 40.3 in | ✓ Yesupright console bar | ✕ NoNo | Check price on Amazon |
3 WalkingPad Denise Austin 2.0Adds side rails | 1 to 7.5 mph | 240 lb | 47 x 17 | 83.8 lb | 56.6 x 29.3 x 39.5 in; folded 38.7 x 29.3 x 7.6 in | ✓ Yesfoldable side handrails | Not published | Check price on Amazon |
Figures are as published by the maker unless the product section below says otherwise. Hover or tap a cell for the full note. We link to the live price instead of printing one, because prices change daily.
If you are still deciding between a pad and a treadmill, our walking pad vs treadmill comparison lays out the trade-offs.
Setup, maintenance and warranty
Setup. The X21 arrives assembled. Unfold the deck, lift the console until it locks, insert the safety key and plug in. Pair the KS Fit app by NFC or Bluetooth if you want app control and session logs.
Maintenance. Wipe the belt and hinge area, check the fold lock before each use, and lubricate the belt at the interval in the manual. Our lubrication guide covers the method. If the belt drifts, see how to center a walking pad belt.
Warranty. WalkingPad.com lists a one-year warranty with an optional extension; KingSmith.com does not print warranty terms on the X21 page. The WalkingPad FAQ says the one-year limited warranty applies to purchases made directly from WalkingPad.com, so if you buy on Amazon or from another retailer, confirm whose warranty applies. WalkingPad.com also lists 30-day returns.
Safety and recalls
No CPSC recall for KingSmith WalkingPad treadmills, including the X21, was listed when we checked on 28 September 2026. Our search of CPSC treadmill recall records returned recalls from Peloton, Nautilus, Johnson Health Tech and older brands, with no KingSmith or WalkingPad entry. The X21 includes a safety key; clip it to your clothing whenever you run, keep children away from the fold hinge, and lock the deck before rolling it.
How we researched this review
We compiled this review on 28 September 2026, using our standard research method and these sources:
- WalkingPad.com X21 product page and FAQ.
- KingSmith.com X21 product page.
- Independent reviews: Treadmill Review Guru (Sydney Kaiser), TreadmillReviews.com and RunToTheFinish (Amanda Brooks).
- Amazon listing titles for the X21 seen in search results (we did not open Amazon pages).
- CPSC recall data for treadmills.