A bucket seat is sized on your hips, not your chest. That is the first thing to unlearn coming from clothing. Everything else follows from one measurement across the widest part of you when you are sat down.
Measure yourself sitting
Standing measurements are no use here. A bucket seat has fixed bolsters and it has to take you as you actually sit in the car.
1Sit on a hard, flat chairFeet flat, knees together, back straight against the chair back. No cushion.
2Measure across your hipsThe widest point, side to side, sitting down. This is the number that decides everything.
3Take your waist tooStanding, around the natural waist. Our seats are listed against this.
4Note your heightAnd whether you are long in the body or long in the leg, because it changes which shell suits.
Measure in what you will wearA race suit, and fireproof underwear under it, adds real bulk at the hips. If you drive in a suit, measure in it. Between two seats, that layer is often what decides it.
Waist size, and what each band means
Every seat on the site is listed against a waist band.
If you are between two bands, take the wider seat. A seat that grips at the hips is uncomfortable within twenty minutes and there is nothing you can do about it afterwards. A slightly wide seat can be padded out with an insert kit or a thicker cover.
Driver height
The second filter. It decides how far up your back the shell comes and where the head support sits relative to your shoulders.
If you are over six foot, filter on that first and then on waist. The tall shells are a much smaller part of the range and it is quicker to start from the shorter list.
Cobra seat dimensions
Cobra publish a dimension drawing for every seat they make, and these are their figures for the bucket seat families. Height is floor to the top of the shell with the base flat on the ground, width is across the widest point, depth is front to back. All in millimetres. The GT versions of the FIA seats are the same shell cut wider across the hips, so if a standard shell is tight, the GT is the next step.
Every Cobra seat listing on the site carries these figures, plus the base width, on its Additional information tab, so you can check the exact model and edition you are looking at. Other brands publish theirs on the listing where available.
Seats sized in inches
The Kirkey aluminium seats and some of the Tillett composites skip the waist bands and give you an explicit seat width instead, measured across the inside of the shell at the hips. That is the most precise way any of these are sold, so if you have measured yourself sitting down you can match it directly.
As a rough rule, take your seated hip measurement and add an inch for a suit. That gives you the internal width you are looking for.
Construction, and how it changes the fit
It is not only about weight. A carbon shell is far stiffer, so the bolsters do not give at all and the seat feels a size smaller than a fibreglass shell on the same nominal band. Push on the bolsters of a cheaper fibreglass shell and you get some flex. On carbon you get none. If you are at the top of a waist band, that difference matters.
Three things to check before you order
Head support or not
About half the range has integrated head support and half does not. A seat without it is lighter and easier to see out of, and it suits a car that already has a headrest or a cage with a rear bar in the right place. A seat with it is the usual choice for circuit and rally work.
Harness holes
Almost every seat here takes a four point harness and most take a six point as well, but not all. The six point needs two extra holes low in the base for the sub straps. It is listed on every product under harness compatibility, and it is worth checking before you buy the harness.
HANS clearance
A good part of the range is listed as HANS friendly, meaning the shoulder openings are cut to clear a head restraint device without the collar fouling the shell. If you already run a HANS or you plan to, filter on it. A seat that is not HANS friendly will physically work but the device sits badly against the shoulder wings.
Side mount or base mountTwo ways a seat bolts in, and they are not interchangeable. Nearly all of our competition bucket seats are side mount, fixing through brackets on the sides of the shell; a few are base mount, bolting down through the seat base. Which one you need depends on the car and the subframe, not on the seat, so read our seat mounting and fixing points guide before you order the brackets.
Approval and dates
Most of the FIA seats we stock are 8855-1999, which is the long-standing competition standard. A smaller number are 8855-2021, the newer one, and a handful are 8862-2009, the tougher standard used in top-level racing. Road and Track seats are not competition approved and are meant for fast road and track day use.
FIA seats carry an expiry date printed on the homologation label. Check what your championship requires and how long the seat has left before you buy, particularly on a discounted older stock item.
Send us your seated hip measurementThat, your waist, your height and the car. Seats are the one thing worth getting right first time, and we will tell you honestly if the one you have picked is going to be tight. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
Waist, height and construction bands are from our product data, checked 2 August 2026. Cobra dimensions and weights are Cobra’s own published figures, read 3 August 2026.
