Air Squats: Form, Depth, Knee Travel and a Path to 3 × 15

An air squat is a squat with no added load: feet about shoulder-width apart, sit your hips down until the hip crease is below the top of your knee, then stand all the way up, with your heels flat the whole time. Your knees can travel forward past your toes as long as they point the same way as your toes.

It is the second rung of the squat ladder, after the box squat, and you clear it at 3 sets of 15 clean reps.

When you are ready for air squats

The squat ladder runs box squat, air squat, split squat. The ladder’s move-up rule for two-leg rungs is 3 sets of 15, so leave the box squat when you can do 3 × 15 to a box at full-depth height (low enough that your hip crease ends below the top of your knee) without pushing off with your hands or dropping onto the seat. Then try 3 × 10 air squats, whichever plan you’re on.

The squat hold in the four-rep test has no pass mark, but it shows whether you can sit at the bottom with heels flat and chest up at all.

How to do an air squat

Set your feet. Heels about shoulder-width apart, toes turned out a little. Hip width or slightly wider is also fine; use whichever lets you reach depth with your heels down.
Brace. Ribs down, chest up, a breath held lightly in your belly.
Sit down between your heels. Hips go back and down at the same time as the knees bend. Reach your arms forward as you go down; they balance you.
Knees follow the toes. They point the same way as your feet and are free to travel forward.
Reach depth. Hip crease just below the top of the knee.
Stand up by driving through the heels, whole foot flat, until hips and knees are fully straight. Arms come back down.

Take about two seconds on the way down and stand up at a steady pace.

A rep counts when the hip crease passes below the top of the knee, both heels stay down, the knees don’t cave in, your back stays in the position it started in, and you stand fully upright at the top. Check your depth once by filming a set from the side. A rep that stops high is a miss; end the set there and log the honest count.

What 21 air squat guides tell you, and where they disagree

We read 21 air squat guides from Google US results and two related web searches, and noted what each one says about setup, reps and when to move on. They agree on less than you might think.

Question	What the 21 guides say
Can the knees go past the toes?	4 say no, 1 warns against “too far”; 4 say yes; 10 only say the knees should track over the toes; 2 don’t say
How deep?	15: below parallel; 4: thighs parallel; 1: “as low as possible”; 1 doesn’t say
How wide?	15: shoulder width; 2: hip width; 3: anywhere from hip to shoulder width; 1 doesn’t say
Which way do the toes point?	12: “slightly out”, no number; 3: straight ahead; 2: depends on your build; 2 give angles (15–30° and 45°); 2 don’t say
How many reps?	9 give sets and reps; 12 don’t
When to move on?	1 gives a rep target for moving to a harder variation; 7 say “once your form is solid”; 13 don’t say

How we got this: on 31 October 2026 we took the article results for “air squats” and “how to do air squats” from Google US, plus pages from two related web searches, and fetched 26 pages. Two blocked our script and three showed almost no text without JavaScript, which left 21.

One person coded each page by hand from its text. This is one day’s snapshot of US results, not every guide on the web.

The biggest split is the knee rule, so it gets its own section below. The depth split is smaller than it looks: 2 of the 4 “parallel” guides say slightly below parallel is fine, and a third sets hips below knees as a target elsewhere on the page. The rep and move-on gaps are what the progression further down is for.

Knees past toes: what the research shows

Keeping the knees behind the toes moves load to the hip and lower back rather than removing it. Fry and colleagues (2003) had seven trained men squat with a barbell equal to their bodyweight, once freely and once with a barrier that stopped the knees moving forward past the toes.

With the barrier, knee torque fell by about a fifth (from 150 to 117 Nm on average) and hip torque rose from 28 to 303 Nm. The lifters also leaned their trunks further forward. The authors concluded that loading the hips and knees appropriately may need the knees to move slightly past the toes.

It is one small study of loaded squats, so read it for direction, not precise numbers. What it supports for your air squats:

Let the knees travel. How far depends on your leg length and ankle mobility.
Watch direction, not distance. Knees pointing the same way as the toes, not caving in.
Keep the heels down. Knees drifting forward with the heels coming up is a fault; knees forward with the heels flat is not.

How deep: what the research shows

A 2013 review by Hartmann and colleagues, covering over 160 papers, concluded that deep squats do not raise the injury risk to the knee’s passive tissues. They found the highest compressive forces and stresses behind the kneecap at about 90° of knee bend. In deeper flexion, the tendon wraps around the end of the thigh bone and the contact area behind the kneecap grows, which spreads the load.

Their condition: the technique is learned accurately under expert supervision and loads go up gradually. Most of the evidence is on loaded squats; bodyweight is the light end of that range.

That is why this rung asks for the hip crease below the knee. If you can’t get there with your heels down and your back in its starting position, you’re not ready to leave the box squat yet. If deep squats hurt your knee, squat to a box at a pain-free height and get the knee checked if the pain doesn’t settle.

Muscles worked

Muscle	Role
Quads	Straighten the knees; the main movers
Glutes	Straighten the hips; work through a longer range the deeper you go
Adductors	Help straighten the hips out of the bottom and steady the knees
Hamstrings and calves	Help steady the hip, knee and ankle
Trunk muscles	Hold the back in position

What goes wrong, and the fix

These are coaching rules of thumb, not tested in studies.

What you see	Likely cause	Fix
Heels lift at the bottom	Ankles run out of range	Widen the stance a little and turn the toes out a bit more; if the heels still lift, go back to the box squat
Knees cave in on the way up	Fatigue, or a stance too narrow for your hips	Push the knees out over the toes and try a slightly wider stance; end the set at the first rep where they cave
Chest drops and you tip forward	Hips going back without the knees bending	Reach the arms forward and sit down between the heels, hips and knees bending together
Reps stop above depth	Mobility, or the set is too long	Squat to a low step as a depth target for a week, then remove it
Hips stop short at the top	Rushing the next rep	Stand all the way up, hips and knees straight, before each rep

The air squat progression

The 30-minute session gives the squat block a rule: add a three-second pause at the bottom before you add reps. Like the tempo lever in the three levers, it makes the same rep harder without changing the exercise. On this rung you alternate two kinds of week:

Normal week: 3 sets at your current reps, normal tempo.
Pause week: the same reps with a 3-second pause at the bottom. Hold the position at full depth, heels down, then stand. The rep standard is the same.

The rule for moving on: when every rep in all of the week’s sessions met the rep standard, take the next step. If any rep missed, repeat the week.

Step	Sets × reps	Tempo
1	3 × 10	Normal
2	3 × 10	3-second pause
3	3 × 12	Normal
4	3 × 12	3-second pause
5	3 × 15	Normal: rung cleared

If every week goes to plan, that is five weeks. Repeating a week is normal. The rung clears at the ladder’s own number, 3 × 15 at normal tempo; the pause weeks are there to get you to it at full depth.

Your first session: try 3 × 10. If you can’t finish it to depth, go back to the box squat until you pass the box gate above. If 3 × 10 was easy, try 3 × 12 next session, then 3 × 15; start at the highest one you complete clean. Clearing it still takes a full week of clean sessions.

Keep the 10 walking lunges per leg that the squat block alternates with your sets. Three sets plus the lunges can run past the block’s 5 minutes, especially in pause weeks; let it run over rather than cutting sets.

After step 5, move on to the split squat rather than adding reps. Putting most of your weight on one leg is how the ladder keeps bodyweight leg work heavy enough to progress.

Where this fits in the plans

Foundation plan: three full-body sessions a week. Use air squats in the squat block of all three, and apply the moving-on rule to all three sessions. The rung can take longer than the plan’s four weeks; if you move to Build first, stay on it there.

Build plan: leg days are Wednesday and Saturday, and the second session of each pair normally runs a rung harder. If you start Build still on this rung, both leg days are air squats at the same step. Once you clear step 5, Saturday moves up to split squats and Wednesday stays on air squats at 3 × 15.

The warm-up in every session already includes 20 air squats; those don’t count toward the progression. Separately, the standards table puts the beginner squat checkpoint at 25 air squats. That belongs on your monthly test day, not in a training set.

Frequently asked questions

What muscles do air squats work?

Mainly the quads and glutes, which straighten the knees and hips as you stand up. The adductors, hamstrings and calves help, and the trunk muscles keep your back in position. Going deeper makes the glutes work through a longer range.

Is an air squat the same as a bodyweight squat?

Yes. “Air squat” is the name common in CrossFit; “bodyweight squat” is the same movement. Both mean a squat with no added load, usually taken to the point where the hip crease is below the top of the knee.

How many air squats should I do a day?

No study sets a daily number. On this site’s squat ladder you train 3 sets two or three times a week, starting at 10 reps and moving up with a pause week before each rep increase. Once 3 sets of 15 are clean, move to split squats instead of adding more reps.

Is it bad if my knees go past my toes when I squat?

Not in itself. In a small study, blocking the knees from moving forward cut knee torque by about a fifth but raised hip torque from 28 to 303 Nm, and the authors concluded the knees may need to move slightly past the toes. What matters more is that the knees point the same way as the toes and the heels stay down.

How low should you go in an air squat?

The usual standard, and the one used here, is the hip crease below the top of the knee with heels flat and your back in the same position as at the top. If you cannot reach that without your heels lifting or your back rounding, train the box squat until you can.