If you've adopted tubeless tires for cyclocross racing and training, you're already aware that sealant is a must. The liquid tire sealant serves two distinct purposes - first, making the tire casing and tire/rim interface airtight, and second, repairing small punctures (like thorns) "on the fly."
But how much tire sealant do you need? If you don't install enough, the tire may not seal; too much, and you're adding needless extra weight and potentially wasting the (expensive) sealant. Let's talk about how much sealant is recommended by manufacturers so you can get it right.
Assumptions
Unless otherwise noted, these recommendations are for common 700x33 cyclocross tires that meet the tire width limit rules. If you're running a wider tire for cyclocross, such as the newer 38mm wide models from Challenge, you'll need more sealant, because there's just more surface area to cover inside the larger tire.
Stan's NoTubes sealant recommendations
Stan's makes one of the most popular sealants on the market, trusted by many riders.
Stan's recommends 55ml of liquid sealant for 700x32 tires (the vast majority of tire brands make 33mm wide cyclocross tires now, not 32mm) so while their labeling is a little outdated, stick with the same 55ml recommendation.
Challenge tire sealant recommendations
Challenge's SMART tire sealant is a popular choice for riders who are running Challenge tubeless cyclocross tires.
Challenge recommends 60-80ml of liquid sealant for tires 30-33mm wide. With 33mm at the top of that range, I'd go with 80ml for a little extra puncture protection.
Caffélatex tire sealant recommendations
Caffélatex is another very popular and widely adopted tire sealant brand.
Effetto Mariposa, the manufacturer of Caffélatex, suggests using 40ml of sealant in a cyclocross tubeless tire, and should you happen to be using their plant-based Végétalex, step it up to 45ml.
Orange Seal tire sealant recommendations
Orange Seal offers 3 distinct sealants, Regular, Endurance, and Subzero. Unfortunately they don't have a specific recommendation for 33mm cyclocross tires.
Their published recommendations are 1-2 fl oz for "road" tires and 3oz for "26" MTB"... so I'd aim for between 2 and 3 fl oz if I was going to experiment with Orange Seal for cyclocross.
Muc-Off tire sealant recommendations
Muc-Off recommends 60 to 75ml for "cross" tires but doesn't list a specific width.
Silva tire sealant recommendations
Silca offers their "Ultimate Tire Sealant" and recommends 65ml for 32mm wide tires. Close enough.
How much does bicycle tire sealant weigh?
We can see that most brands recommend 40-60ml of sealant for a 700x33 cyclocross tire. For reference, 60ml is almost exactly 2 fl oz.
If you're shaving grams you might be interested in knowing how much that sealant weighs. Varying slightly based on the density of the sealant you select, but 1 gram per ml looks like a reasonable average based on my tests, so if you're adding 60ml of sealant to a tubeless tire that's about 60 grams of sealant.