How to Measure Sit Bone Width for a Bike Saddle Fit

Your sit bones are the two bones you can feel pressing into a hard chair, and the distance between them is the one measurement that decides whether a bike saddle can be comfortable. It takes ten minutes, a piece of cardboard and a ruler, and it is the difference between buying a seat and guessing one.

What you need

• A sheet of corrugated cardboard, the kind boxes are made of. A folded towel will not hold two clean dents.
• A hard, flat chair. A padded seat spreads the load and blurs the marks.
• A ruler or tape measure marked in millimetres.
• A pen.

The measurement, step by step

1. Put the cardboard on the hard chair and sit on it.
2. Sit the way you ride. If you ride upright, sit upright. If your bike has you leaning forward, tilt your pelvis forward a little, as if your hands were on the bars. One saddle maker’s instruction is to hold your riding posture for 10 to 15 seconds and specifically not to sit back as if in an office chair.
3. Lift your feet slightly so your full weight is on the cardboard for those seconds.
4. Stand up and look for two dents. Circle each one and mark its centre.
5. Measure centre to centre in millimetres. Not edge to edge: measuring the outside of the dents inflates the number, and the makers’ charts linked here are all built on the centre figure.
6. Do it again on another day, same chair, same posture. If the two readings differ by a few millimetres, keep the wider one.

Bike shops do the same thing on a gel pad; the corrugated cardboard method is the same measurement at home.

What to add to the number

A saddle is wider than your sit bones, so the makers add an allowance. The makers do not agree on one figure; the fitting trade writes the relationship as width of sit bones plus an amount defined by the manufacturer, and the amounts on the makers’ own pages differ:

Whose rule	What it says	Example
Bike-fitting trade rule of thumb	Add about 20 mm	110 mm sit bones → 130 mm saddle (the rider in the example chose 145 mm for more support)
BiSaddle	120 mm sit bones suggests a 140 to 150 mm saddle	Add 20 to 30 mm
WTB fit tool	Enter a sit bone width from 80 to 170 mm and it matches it to WTB’s saddle sizes	Its Wide saddles are 150 mm; the Comfort is labelled Extra Wide at 174 mm

The direction of the difference matters more than the exact figure. The allowance is for the part of the saddle that curves away at the sides and cannot carry weight, and the more upright you sit, the more of your weight lands squarely on the sit bones and the more width you want under them. Leaning forward, add about 20 mm. Sitting upright on a city bike or a home exercise bike, add more.

Where your number lands on the shelf

Once you have a saddle width, here is what is actually on sale at it, from the makers’ own product pages on 19 September 2026:

Saddle width	Saddles at that width	Who they suit
130 to 160 mm	Fizik road saddles in 130 to 160 mm, WTB Koda in 145 or 150 mm	Riders leaning over drop or flat bars
163 to 174 mm	Terry Liberator X 163 mm, Brooks C17 164 mm, Terry Cite Y 173 mm, WTB Comfort 174 mm	Hybrids, slightly forward
200 to 227 mm	Brooks C67 200 mm, Brooks B67 205 mm, Selle Royal Respiro Relaxed 227 mm	Fully upright
Adjustable 100 to 240 mm	BiSaddle Health+	Anyone still unsure of the number

If your sit bones plus allowance come out above 180 mm, you are shopping in the bottom two rows, and the racing and hybrid saddles in the first two rows will be too narrow for you. Our guide to the most comfortable bike seat goes through seven of the wide ones, with the weight, price and the catch for each.

The condition attached to the whole method

The cardboard measurement assumes a sit-up-straight posture, and the fitting trade is candid that most cyclists ride with some degree of pelvic bend, in which case the sit bones stop being the main pressure point. Read that the right way round: the more upright you ride, the better the measurement describes where your weight actually is. On an upright commuter, a cruiser or an exercise bike at home, it is describing you exactly.

What the number does not settle

• Padding. Width first, padding second; our seat guide has two makers’ own words on why thick gel stops helping on a long ride.
• The bike’s own limit. A saddle can be swapped; a frame’s rated user weight cannot. Ten bikes with published limits of 330 lb and up are in our guide to heavy duty exercise bikes.
• Whether you will like it. Sit on it for an hour indoors before you decide, and check the return terms first.

More of our measured guides are in the sports gear section.

Where these numbers come from

The method and the plus-20 mm rule of thumb are from BikeFit’s fitting guide and the posture and timing details from BiSaddle’s, both linked above; both companies sell fitting products or saddles. Saddle widths and the WTB tool’s input range are from the makers’ pages on 19 September 2026.

Frequently asked questions

How do I measure my sit bone width at home?

Put a piece of corrugated cardboard on a hard chair, sit on it in your riding posture for 10 to 15 seconds, stand up, and mark the centre of the two dents. Measure between the two marks in millimetres. That centre-to-centre distance is your sit bone width. Do it twice on different days and keep the wider reading.

How much do I add to my sit bone width to get a saddle width?

It depends on whose saddle you are buying and how upright you ride. One fitting company's rule of thumb is to add about 20 mm; one saddle maker says a 120 mm sit bone width suggests a 140 to 150 mm saddle. Leaning forward, add roughly 20 mm; sitting upright, add more, because more of your weight lands on the sit bones.

What is a normal sit bone width?

Saddle makers' fitting tools accept measurements from about 80 mm to 170 mm, and saddles on sale run from 130 mm for racing to 240 mm for fully upright riding. There is no correct number; there is only yours, and the saddle width that follows from it.

Does sit bone width matter if I lean forward on the bike?

Less than it does for an upright rider. The measurement assumes a 90-degree, sit-up-straight position. The more you rotate your pelvis forward, the more your weight moves off the sit bones and onto the front of the pelvis, which is why road saddles run narrower for the same sit bones.