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Diono Monterey 5iST FixSafe

The Diono Monterey 5iST FixSafe is 17 in wide, weighs 18.7 lb, and has a booster weight limit of 120 lb, per Diono. A fold-flat high-back booster that collapses to carry-on size, with a 12-position adjustable headrest and backrest.

  • $259.99List price
  • 120 lbBooster to
  • 18.7 lbSeat weight
  • 17 inWidth
See it on Diono's site

When does it expire?

All booster seats

Monterey 5iST FixSafe: key facts

  • The Diono Monterey 5iST FixSafe works as a booster from 40 to 120 lb and 38 to 63 in tall, per Diono.
  • Outgrown by height: "Use ONLY with children whose ears are below the top of either the fully raised booster seat head support or the fully raised vehicle headrest."
  • It installs with LATCH or seat belt.
  • Diono says it expires 8 years after the date of manufacture.
  • Diono says it isn't certified for aircraft.
  • It's 17 in wide at the widest point and weighs 18.7 lb.

From Diono's manual and published specs. Always follow the limits on your seat's labels.

How the Monterey 5iST FixSafe stacks up

Against the 65 booster seats we track. The shaded band is where the middle half of them fall; the dot is this one.

Booster weight limit120 lbHighest booster limit of 64 booster seats

Within the typical range for booster seats (100 lb to 120 lb).

This one
100 lbmiddle 110 lb120 lb
Expiration8 years

Within the typical range for booster seats (8 years to 10 years).

This one
6 yearsmiddle 10 years12 years
Width17 in7th narrowest of 31

Within the typical range for booster seats (17 in to 18.6 in).

This one
10.2 inmiddle 17.3 in23.2 in
Weight18.7 lb40th lightest of 42

Above the typical range for booster seats (6 lb to 13.2 lb).

This one
1.8 lbmiddle 9.8 lb20.9 lb
Price$259.9948th lowest price of 53

Above the typical range for booster seats ($55.99 to $159.99).

This one
$19.98middle $79.99$399.99

What sets the Monterey 5iST FixSafe apart

Measured against the 65 booster seats we compare, from each maker's published specs.

  • 7th narrowestof the 31 booster seats with it published: 17 in
  • Weight: 18.7 lbabove the middle half of the 42 booster seats that publish it (6 lb to 13.2 lb)

Next to its closest matches

Flying with the Monterey 5iST FixSafe

Diono's label: “THIS RESTRAINT IS NOT CERTIFIED FOR USE IN AIRCRAFT. Aircraft seats do not have shoulder belts which are required for use with this child restraint.” American lists “Booster seats with no approval label or shoulder harness” under seats and devices not approved for use on board (source).

What airlines say about car seats:

  • American: “Each ticketed customer is allowed 1 stroller and 1 car seat to be checked free of charge” “If an unoccupied, adjoining seat is not available, the gate agent will check the safety seat to your final destination.” Source
  • Alaska: “We will transport your child's car seat and stroller free of charge as checked baggage.” Source
  • JetBlue: “Checking a child safety seat will not count towards your checked baggage allowance and there is no fee assessed” Source
  • Spirit: “One (1) car seat will be accepted per child as checked baggage at no charge.” Source
  • Frontier: “strollers and car seats can be checked for free.” Source
  • Allegiant: “There is no charge for checking or gate checking one car seat per fare-paying passenger.” Source
  • Breeze: “Child seats may be carried on board the aircraft if a seat has been purchased for the Infant or Child” Source

Quoted from each airline's page as of 2026-11-02.

Listed features

  • Folds small for travel and carries on
  • Narrow 17 in width
  • Wide 40 to 120 lb range
  • One-hand 12-position adjustment

Worth checking

  • Heavy at 18.7 lb for a travel booster
  • Fairly high regular price

Where to buy the Monterey 5iST FixSafe

Prices and availability change. We may earn a commission from some links.

good to know
  • Check for recalls: Search the agency's recall list with the model number and date code from the label: NHTSA recall search.
  • Car seat use and installation: see NHTSA's car seat page, which also lists free car seat inspection by certified technicians. Check the label and the maker's instructions, and ask your pediatrician about your child.

Full specs

Diono Monterey 5iST FixSafe
TypeBooster
List price$259.99
Booster weight40–120 lb
Booster height38–63 in
Seat weight18.7 lb
Width17 in
Head ruleUse ONLY with children whose ears are below the top of either the fully raised booster seat head support or the fully raised vehicle headrest.
InstallationLATCH, seat belt
Load legNo
Anti-rebound barNo
RotatesNo
Aircraft labelNot certified for aircraft
Expires after8 years

Compare the Monterey 5iST FixSafe with

How each closest rival differs from the Monterey 5iST FixSafe, from the makers' specs.

Ask the meadow

Monterey 5iST FixSafe: questions answered

From Diono's published specs, last checked 2026-11-06.

Will the Diono Monterey 5iST FixSafe fit three across or in a small car?

It's narrower than 66% of the boosters we track, at 17 in. The narrowest is the Mifold Comfort Grab-and-Go Booster at 10.2 in. Fit depends on your vehicle; check each seat's manual and your vehicle manual. Car seat use and installation: see NHTSA's car seat page, which also lists free car seat inspection by certified technicians. Check the label and the maker's instructions, and ask your pediatrician about your child.

Can you bring the Diono Monterey 5iST FixSafe on a plane?

Diono doesn't list it as certified for aircraft, so it can be checked as luggage but not used in the plane seat. See seats approved for planes.

Monterey 5iST FixSafe or Hifold: what's different?

By the makers' specs, the Hifold lists for $10 less. See every spec side by side.

Is it OK to buy a used Monterey 5iST FixSafe?

NHTSA publishes guidance on used car seats on its car seat page. Diono lists a lifespan of 8 years from manufacture for this model. Check the label and the maker's instructions, and ask your pediatrician about your child.

Still wondering? Write to us at hello@cribpicks.com and we'll look it up.

More booster seats

Where these specs come from

Last checked 2026-11-06. Spot something wrong? Tell us. Read our editorial and safety policy and corrections.