My bike has 700x32 tires. Interested in trying out wider tires 35-42mm. My standover is pretty close right now, very little clearance. If I switch to 42mm tires, which are around 10mm wider, will the bike's standover height also increase by 10mm?

The extra 10 mm in width is 5 mm on each side. So maybe 5mm in the radial direction, too.

However,

Sheldon Brown has a computer calibration chart, showing
700x32 at 2155mm circumference,
700x44 at 2224. (Computers count the distance of each revolution on the ground)

Circumference = Pi*radius*2, so the radius = C/2/Pi

2155 gives radius of 343 mm (googling "343*2 mm in inches" gives 27.008 inches. That sounds about right.)
2224 gives radius of 354 mm

That's interesting, 11 mm difference. More than I would expect. Tires do flatten out at the contact patch, so maybe that helps reduce the difference?

(Cateye says 32mm is 2155, 40mm is 2200. That's 7mm height difference.)

thanks for doing the math! maybe I'll give 35's a try .

Circumferences/diameters indicated for cycle computers are (should be) for loaded tires. They will be less than stand over height (which is based on unloaded tires).

The maximal width of a tire (the center of the circular cross section) is on a circle with a circumference/diameter larger than the rim side walls. That means the addition to the stand over height is > 1/2 the tire width (and < the tire width). It's not clear if it's going to be closer to one or the other.

If it's a road bike, it likely doesn't matter if the stand over height is a bit more than optimal with the larger tires and the original stand over was OK (that is, it would be a problem only if the stand over was too large with the narrow tires).