You could use a pair of calipers. Alternatively, measure its circumference using a piece of string and divide the measure by pi.
Internal diameter.
The radius of a circle is half the diameter.
with a big tape measure
I have No Clue........
You measure it.
Mercury's diameter from pole to pole is approximately 4,880 kilometers.
The exact diameter of the geographic north pole (like the south pole) is in theory zero.
The diameter of the Moon is approximately 3,474.8 kilometers.
For the width, measure the length of the track or pole and add an inch for overlap in the middle. The height should be measured from the top of the track or the small metal ring for a pole.
To measure a curtain ring, you would typically measure the diameter of the inner circle on the ring. This measurement will help you determine the size of the curtain rod or pole that the ring will fit onto.
Jupiter has about 1/10 the diameter of the Sun. Note that due to its fast rotation, there is a fairly large difference in the diameter, depending on whether you measure from pole to pole, or from equator to equator. Jupiter also has about 1/1000 the volume of the Sun, and 1/1000 of the Sun's mass.
Internal diameter.
The Earth has a diameter of about 12,742 kilometers, which is equivalent to 12.742 million meters.
The diameter of the Earth from North pole to South pole is 7,899.83 miles. This is only 25 miles less then the distance around the equator, which is 7,926.41.
The best way to find a suitable replacement pole for an umbrella is to measure the length and diameter of the existing pole, and then search for a replacement that matches those measurements. You can also check with the manufacturer of the umbrella for specific replacement parts.
A 'metal pole' could be made out of so many different types of metal, but most likely the metals you are looking for are Iron, Steel or a Chrome-plated pole.
Internal diameter.