Questions? Call...800.591.8907

16 Years Serving Customers Like You. Buy With Confidence.

Engineering Supplies, Blueprint Storage, Measuring Tools, Surveying Equipment & More!

Using a Planimeter (Area Measuring Tool) with Drawing Scales

A planimeter will give correct results for "any" scale factor whatsoever, at least within the tolerance imposed by the operator and a small mechanical uncertainty.

In practice, an operator will trace an area on a plan with a known scale factor, and then multiply the "raw" planimeter reading by a constant, Ca, to get a corrected reading.

The constant Ca can be computed using an equation given in the instructions that come with each instrument. It is Ca = u*Sc^2 . "u" is the number of square inches per planimeter count, unique for each instrument and dependent on the arm length of that instrument. It is provided with each instrument shipped. Sc is the scale factor of the drawing to be measured.

For example, suppose an Operator is using a planimeter with its arm length set to medium length. He or she should refer to the calibration record that comes with the instrument and find that u is 0.017324 for a medium arm. The operator sees that the scale factor for his or her drawing is 1:400, meaning 1 unit = 400 units, where a unit can be an inch, a foot, or whatever. For this example the operator wants his answer to be in square feet so he must convert his 1:400 scale to the number of inches per foot. Since 1inch = 400 inches, it also equals 400 divided 12, or 33 1/3 feet. The hard part over, he or she uses the equation and finds that Ca equals 0.017324*(33 1/3)^2 , or 19.249.

If the operator has a digital readout, he simply keys in his scale factor of 19.249 and begins measuring. His answer will be in terms of square feet for each measurement. If the Operator has a mechanical planimeter, he or she must manually multiply each planimeter reading by
19.249 to get the number of square feet. If he or she stores the 19.249 in a calculator memory, this task becomes easier.

Some planimeters also give the value of u for metric measurements, that is, u is the number of square centimeters per planimeter count. In this case, the operator might have to convert the scale factor to give the number of centimeters per meter or whatever before computing Ca.

Disclaimer;  By reading this guide on our website, you agree to not hold anyone responsible for any misuse or misunderstandings that you may make. does NOT assume any responsibility with providing this information.

Copyright © 2005 - The Product Team

Factory-Authorized Dealer For The Most Trusted Brands In The Industry

Aervoe Inverted Spray Paint LaserLine Cut and Fill Grade Rods Dahle Paper Trimmers and Shredders Alvin Drafting and Art Products Topcon Rotary Laser Levels and Detectors Brookside Design Premium Brand Blueprint Stands, Clamps, and Racks Doc Box Permit Holders and Boxes DuraWheel Distance Measuring Wheels Futtura Surveyors Equipment and Instruments Alumicolor Scales and T Squares AGL Laser Levels and Pipe Lasers Calculated Industries Construction Calculators and Tools Schonstedt Underground Location Equipment Johnson Level Tools and Equipment Mayline Office Products, Cabinets, and Blueprint Stands Dunham and Morrow Magnetic Ferro Locators Bosch Tools and Measuring Equipment Safco Office Furniture and Products Seco Land Surveying Equipment and Products Agatec Laser Levels Crain Grade Rods Dietzgen Paper and Media Subsurface Instruments Underground Utility Locators Ulrich Plan File Cabinets Neolt Large Paper Trimmers Advanced Organizing Systems Blueprint Storage Boxes and Systems CST Berger Surveying Equipment Artograph Tracing Projectors and Products Dutch Hill Surveyors Tripods Keson Measuring Wheels and Measuring Tapes RotaTrim Rotary Paper Trimmers Elan Field Books and Engineering Log Books SitePro Surveying Supplies
View All Brands

Join Today and we'll send you a coupon to use on your first order!

Please Wait... processing