A fairly good approximation to the rolling circumference of a bike tire is to assume the tire has a circular cross section. If the named width is correct the circumference can be calculated by (rim diameter+(2* tire width))* Pi

For a 700-32 the estimate is (622+(2*32)* 3.14159... = 2155 mm or about 99.2% of your current value. Realistically a lot of "32" tires are a bit smaller so a true roll-out measurement is still the most accurate method.