Underestimate?
The underestimate comes to mind.
over-estimate
estimate
When you estimate something the word that is commonly used the most is "about". This word is saying that it is not an exact measurement.
Estimate
Estimate
Well it is not exact but about 1000 times that's an estimate
I estimate the work on the house will be substantially higher than the estimate the builder submitted.
not desirable
more than less
Less or more
conversant