Measurement: Converting to Foot to Inches PDF

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Summary

Measurements exercises and converting foot to inches...

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Converting to Foot-Inches Many industries, especially almost anything in construction, still use the U.S. Customary system for distance measurements, such as the commonly used foot-inch measurement, where inches is written as a fraction. So instead of writing 14’ 3.5”, you would see 14’ 3 ½”. Notice the single quote after the 14 to denote feet and the double-quote after the 3 ½ to denote “three and a half” inches. Important! The denominator for inch fractions starts at 2 and doubles (in this AMAT 240 class, we will not do finer measurements then 1/32 of an inch). So for example:

You would not have an inch written as 3/7 or 9/13 for example. Generally speaking, you would almost always take the measurement in the above fraction style in the first place, but in some cases you do need to convert an S.I. unit or decimal foot value to the fraction style. What makes this a bit awkward is that the decimal version of a number is in base 10, but you have to convert to a denominator that isn’t (see the above fractions).

Steps to Convert Let’s work through an example to convert a person’s height from cm to foot-inches. Let’s say the person is 165cm tall. 1. Convert the cm to feet. Use your conversion sheet to find the correct factor. We will round the answer to the nearest tenth to avoid a long string of decimal places. 165 / 30.48 = 5.4 feet The 5 is a whole number, so 5 feet. The 0.4 represents a partial foot, thus this is the inches portion. However! The 0.4 is still in the unit of feet at this point! Let’s set aside the 5 for now as that’s a whole number, and we’ll continue working with the 0.4. 2. Convert the 0.4 feet to inches, so look in the conversion table to find the correct factor to convert feet to inches, which is 12:

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So we have 4.8 inches, but this is still not the common way to write it. Similar to the above, we can ignore the 4 for now, as that is whole inches. In the next step, we’ll convert the 0.8 to a fraction, and then we can write the answer the common way. 3. Establish the precision of the measurement; your questions will provide this. Let’s say we need the answer to the nearest 1/8 (one-eighth) of an inch, so multiply the 0.8 by 8 (the denominator of our precision):

4. Round the answer to the nearest whole number, so 6.4 becomes 6. 5. Place the value over the 8, and simplify / reduce if possible:

So even though the precision was 1/8”, you should still simplify or reduce to ¾”. 6. Complete your answer by including the whole numbers (5 for the foot and 4 for the inch) we put aside earlier: 5’ 4 ¾”

Or: 5 ft. 4 ¾ in.

Or: 5 feet 4 ¾ inches

The first way to write the answer is likely the most common way, so try to keep to that.

Practice Questions 1. Convert 83cm to foot-inches. Round answers to the nearest hundredth. 1/16” precision.

2. Convert 0.625 inches to fraction form, 1/8 inch precision.

3. Convert 121.39 feet to foot-inch form. 1/16” precision.

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4. Convert 877.2 feet to meters. Round to the nearest hundredth.

5. A contractor measured the perimeter of a fence to be 247.9 meters. Fence material costs $2.58 / foot. How much fence material does the contractor need (answered in footinch, do not round calculations)? How much would the fence material cost? Careful! You can only buy in whole feet.

6. Convert 10.4mm to inches in fraction form, 1/32” precision. Round all calculations to the hundredth.

7. Harold is working on a hobby project and needs a few pieces of wood, which are the following lengths: 2’ 2 ½”, 1’ 8 ¾”, and 3’ 7/8” What is the total amount of material needed in foot-inch?

8. Convert 54 inches to mm. Round to the whole mm.

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Answers: 1. 83 / 30.48 = 2.72 ft 0.72 * 12 = 8.64 0.64 * 16 = 10 (round this one to the nearest whole) Ans: 2’ 8 10/16” but need to simplify: 2’ 8 5/8” 2. 0.625 * 8 = 5 Ans: 5/8” 3. 121.39 feet 0.39 * 12 = 4.68 0.68 * 16 = 11 Ans: 121’ 4 11/16” 4. 877.2 / 3.28 = 267.44 m 5. 247.9 * 3.28 = 813.112 feet 0.112 * 12 = 1.344 0.344 * 8 = 3 First answer: 813’ 1 3/8” Second answer: 814 * 2.58 = $2,100.12 6. 10.4mm is 1.04 cm 1.04 / 2.54 = 0.41 0.41 * 32 = 13 Ans: 13/32” 7. Add fractions of an inch first: ½ + ¾ + 7/8 = 2 1/8” Add whole inches next: 2 + 8 = 10 inches Add the first step to the second step 10” + 2 1/8” = 12 1/8”, but you cannot have 12” as that is equal to one foot, so you get 1’ 1/8” Now add the feet: 2 + 1 + 3 = 6’ Add this answer to the step above: 6’ + 1’ 1/8” = 7’ 1/8”  is the answer

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8. 54 * 2.54 = 137.16cm * 10 = 1,371.6mm, so rounded: 1,372mm

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