If you need three car seats in one row, or one seat in a small back seat with passengers beside it, every inch counts. These three convertible seats are all listed by their makers at about 17 in wide, and all rear-face to 50 lb. We built this guide from manufacturer specs, NHTSA and AAP guidance and federal recall records; we haven’t installed or measured the seats ourselves. For a broader look at convertible seats, see our convertible car seat guide.
The widths, as each maker states them
| Seat | Width (manufacturer’s figure) | Rear-facing | Forward-facing | Seat weight |
|---|---|---|---|---|
| Clek Fllo | Seating width 16.9 in; base width 13 in | 14–50 lb, 25–43 in (from 5 lb with Clek’s insert) | 26.5–65 lb, 30–49 in | 25 lb (28 lb with anti-rebound bar) |
| Britax Poplar | 17 in (“slim 17 in design”) | 5–50 lb, 18–49 in | 30–65 lb, 35–49 in | 27.2 lb |
| Evenflo Revolve360 Slim | 16.9 in wide (assembled: 16.9 W x 24.3 H x 21.0 D in) | 4–50 lb, 17–48 in | 30–65 lb, 35–49 in | 28.2 lb with base |
Don’t read too much into a tenth of an inch. Makers don’t measure width the same way, and none of these three product pages says exactly where its figure is taken: at the widest point of the shell, with or without cup holders, or across the base. Clek is the only one that gives the seat and the base separately. A seat that’s wide at shoulder height but narrow at the base can sit differently next to its neighbor than a seat that’s wide at the bottom. On paper, these three are effectively the same width. Real-world fit comes down to shape and to your car.
Will three seats fit across in your car?
Nobody can promise that from a spec sheet, us included. Even Britax, which says the Poplar is designed to fit three across, adds that it can’t guarantee three-across fit in every vehicle. Fit depends on:
- Your back seat’s usable width, including how much the doors and side bolsters curve inward.
- Where the seat belt buckles sit. Buckles can end up under a neighboring seat, where they’re hard to reach or press against the car seat, so check the buckle stalks in all three positions.
- Where your lower anchors are. NHTSA notes that lower anchors are found in at least two rear seating positions, which often means not all three. Use lower anchors only in the positions your vehicle manual allows. In a three-across row you may need seat-belt installs; Clek itself describes seat-belt installation as common for three-across and center-seat installs.
- Which seats sit next to each other. Pairing two slim convertibles with a booster or an infant seat changes everything, and some combinations fit only in a certain order.
- Front-to-back room. Rear-facing seats also need depth. Clek lists 32.5 in front-to-back for the Fllo rear-facing with its anti-rebound bar (29 in without it), so check that front passengers still have room.
- Swivel clearance. A rotating seat like the Revolve360 Slim needs space to turn. In the middle of a tight row, check that it can actually swivel.
Before you buy, measure your back seat, read the child seat section of your vehicle manual, and if you can, try the seats in your car before the return window closes. Whatever you choose, each seat must be installed with either the lower anchors or the seat belt, not both, unless the seat’s manual says otherwise, and NHTSA advises reading the vehicle owner’s manual as well as the car seat manual. Then have a certified child passenger safety technician (CPST) check the installation: NHTSA’s car seat inspection station finder helps you find one; NHTSA says technicians check seats free of charge in most cases.
Rear-facing in a slim seat
A slimmer shell doesn’t change the advice. NHTSA says children under one should always ride rear-facing, and children aged one to three should stay rear-facing as long as possible, until they reach the top height or weight limit of their seat. The AAP’s policy statement also recommends rear-facing as long as possible. All three picks rear-face to 50 lb, but children often outgrow a seat by height before weight, so note the height limits: 43 in for the Fllo, 48 in for the Revolve360 Slim and 49 in for the Poplar. Our guide to how long to ride rear-facing explains why it matters.
Recall check (October 17, 2026)
We searched CPSC’s recall database and NHTSA’s recall data for each seat. We found no open recall affecting seats made now, but two of the three have past recalls:
- Clek Fllo: NHTSA recall 21C005000 (December 2021) covered Fllo model numbers FL15 to FL19 made before May 21, 2021, because a child could pick foam from under the seat pad. Clek sent a free plastic insert. Current production falls outside that date range.
- Britax Poplar: we found no CPSC or NHTSA recall naming the Poplar. A 2024 Britax recall for incorrect labels covered the One4Life Slim, a different seat.
- Evenflo Revolve360 Slim: NHTSA recall 25C010000 (September 2025) covers Revolve360 Slim and Gold Revolve360 Slim seats made from December 1, 2022 to December 8, 2024: headrest foam could be picked off and become a choking hazard. Evenflo sends a free tape seal and instructions. Check the manufacture date on the seat’s label.
No CPSC recall named any of the three seats. A clean search isn’t a guarantee, so register your seat with the maker and check for recalls on any seat you’re handed down. Our Britax Poplar vs Evenflo Revolve360 Slim comparison puts those two side by side, and the car seats hub has the rest of our car seat guides.
Our verdict
If three-across is the goal, start with the Clek Fllo: it’s the only one of the three designed around three-across, with a 13 in base and lock-offs for seat-belt installs. Choose the Britax Poplar if you want more rear-facing height and a seat-belt install that doesn’t depend on how hard you pull. Choose the Evenflo Revolve360 Slim for an outboard seat when loading a toddler is the problem, not width. In every case, treat fit as unconfirmed until the seats are in your car and checked by a technician.
Frequently asked questions
What is the narrowest convertible car seat?
Among the seats we verified, the Clek Fllo and the Evenflo Revolve360 Slim are both listed at 16.9 in wide, and the Britax Poplar at 17 in. Clek also lists a 13 in base. Because makers measure width differently, treat these as roughly equal and judge by how they fit your car.
What’s the best convertible car seat for three across?
The Clek Fllo is the one of our picks its maker says is purpose-built for three-across. But whether three seats fit depends on your vehicle, its buckle and lower anchor positions, and the seats beside it, so measure, try the seats in your car and get the install checked.
Can I use lower anchors for all three seats?
Often not. NHTSA notes that lower anchors are found in at least two rear seating positions, so many cars don’t have a set for every seat. Use lower anchors only where your vehicle manual allows, and install the other seats with the seat belt. Also note that Britax and Evenflo rate their lower anchors only up to a 35 lb child.
Is a slim car seat less safe?
Not because it’s slim. Every car seat sold in the US must meet the same federal child restraint standard, FMVSS 213. What matters most is that the seat fits your child, fits your car and is installed tightly and used correctly every time.
How long can my child rear-face in a slim convertible seat?
Until they reach the seat’s rear-facing weight or height limit, as NHTSA and the AAP advise. All three picks allow 50 lb rear-facing; the height limits are 43 in (Fllo), 48 in (Revolve360 Slim) and 49 in (Poplar).
