Height Formatting

Decimal Height vs Fraction Height: What's the Difference?

Decimal height and fraction height express the same measurement in 2 different number formats. Fraction height uses feet and whole inches separated as 2 values — for example, 5 feet 7 inches (5'7"). Decimal height expresses that same measurement as a single continuous number in feet — for example, 5.5833 ft. These 2 formats look similar but produce different values when misread.

The difference between decimal height and fraction height matters across 4 main areas: filling out official forms, reading construction blueprints, entering data in digital health systems, and converting height between unit systems. Writing 5.7 instead of 5'7" is one of the most common height notation errors — and it creates a 1.4-inch (3.56 cm) discrepancy that affects medical records, Body Mass Index (BMI) calculations, and database entries.

This guide covers what decimal height and fraction height are, 3 key differences between the 2 formats, 3 common conversion mistakes with exact values, formulas to convert in both directions, and 3 real-world examples with side-by-side comparisons.

Quick Answer: Decimal vs Fraction Height

What Is Decimal Height?

Decimal height is a height measurement expressed as a single decimal number in feet. The integer part represents whole feet, and the decimal part represents the remaining fraction of a foot converted to a decimal value.

Decimal height is the standard format in computer-aided design (CAD) software, building information modeling (BIM) tools like Autodesk Revit, and construction calculation systems. The American National Standards Institute (ANSI) and International Organization for Standardization (ISO) both permit decimal notation for dimensional measurements in technical documentation.

Example of Decimal Height (5.7 ft)

5.7 ft in decimal height means 5 feet plus 0.7 of a foot. To find the inch value: 0.7 × 12 = 8.4 inches. So 5.7 ft = 5 feet 8.4 inches (173.74 cm or 1.7374 m), not 5 feet 7 inches.

Why Decimal Height Is Used

Decimal height is used in 4 main professional contexts:

• CAD and architectural software: AutoCAD, Revit, and SketchUp store all dimensions as decimal values for computational precision.
• Engineering and manufacturing: Decimal notation supports precision tolerances to 3 or more decimal places. A machined part might require a height of 5.625 ft (5 ft 7.5 in).
• Surveying: Total station instruments output decimal feet by default. A surveyed height of 5.583 ft is standard in survey data files.
• Construction calculators: Digital construction calculators accept decimal feet for staircase riser calculations, framing measurements, and roofing layouts.

What Is Fraction Height?

Fraction height is a height measurement expressed as feet and whole inches as 2 separate values. The foot value is a whole number, and the inch value is a whole number from 0 to 11. The term "fraction height" refers to the fact that the inches portion represents a fractional part of a foot (7 inches = 7/12 of a foot).

Fraction height is the standard format for human height measurement in the United States (US), United Kingdom (UK) informal use, and most English-speaking countries. Medical forms, government identity documents, and sports statistics all record height in feet and inches.

Example of Fraction Height (5'7")

5'7" means 5 feet and 7 inches. The total height in inches is (5 × 12) + 7 = 67 inches. In centimeters: 67 × 2.54 = 170.18 cm (1.7018 m). In decimal feet: 5 + (7 ÷ 12) = 5.5833 ft.

Why Fraction Height Is Used

Fraction height (feet and inches) is the everyday standard in the US because the imperial system (United States customary units) divides linear measurement into feet and inches. Tape measures, rulers, and growth charts in the US display markings in feet and whole inches. The format requires no decimal conversion and matches the physical marks on standard measuring tools.

Decimal Height vs Fraction Height: Key Differences

Accuracy and Precision

Decimal height supports unlimited precision. 5.58333... ft can extend to any number of decimal places. Fraction height is precise to the nearest whole inch (1 inch = 2.54 cm). For human height measurement, whole-inch precision is sufficient. For machined parts, architectural dimensions, or woodworking cuts, decimal precision is required.

Human Readability

Fraction height is readable without calculation. A person told they are 5'7" understands the measurement. A person told they are 5.5833 ft must perform a mental conversion. In health records, patient communication, and identity documents, fraction height (feet and inches) reduces interpretation errors.

Decimal height requires a reference point. The decimal 0.5 in 5.5 ft means 6 inches only if the reader knows that 0.5 × 12 = 6. Without that context, 5.5 ft looks like 5 feet 5 inches to most readers.

Where Each Format Is Used

Common Conversion Mistakes

5.7 ft Is NOT 5'7"

Writing 5.7 as a shorthand for 5'7" is the most common height notation error. The 2 values differ by 1.4 inches (3.56 cm):

This error appears in medical records, dating profiles, and sports databases. A BMI calculated from 173.74 cm vs 170.18 cm produces a different result. For a person weighing 70 kg (154.3 lb): BMI at 170.18 cm = 24.2, BMI at 173.74 cm = 23.2. That difference shifts the BMI category boundary for some individuals.

Confusing Decimal Feet With Inches

Readers often misread decimal feet as feet and decimal inches. The decimal 0.75 in 5.75 ft means 9 inches (0.75 × 12 = 9), not 7.5 inches. This confusion produces measurement errors in construction and carpentry, where a 1.5-inch mistake in a door frame or staircase riser has structural consequences.

The correct reading of any decimal foot value: multiply the decimal portion by 12 to get inches. Never read the decimal digits directly as an inch value.

Incorrect Rounding

Converting 5'7" to decimal feet produces 5.58333... ft (repeating). Rounding this to 5.58 ft and then converting back gives 5 feet 6.96 inches — a loss of 0.04 inches (1 mm). For a single height measurement, this is negligible. But in construction calculations with 50 repeated measurements, the cumulative error reaches 2 inches (50.8 mm), which violates building code tolerances.

Round decimal feet to 4 decimal places minimum in technical calculations. Use 5.5833 ft, not 5.58 ft.

How to Convert Between Decimal and Fraction Height

Fraction (Feet + Inches) to Decimal Feet

To convert fraction height to decimal height, divide the inches by 12 and add the result to the whole feet value.

Decimal Feet to Feet and Inches

To convert decimal height back to fraction height, separate the integer part (whole feet) and multiply the decimal part by 12 to get inches. Round to the nearest whole inch for human height use.

Which Format Should You Use?

Forms and Applications

Use fraction height (feet and inches) on all official forms. US passport applications, Department of Motor Vehicles (DMV) license forms, and medical intake forms require height in feet and whole inches entered as separate numeric values. Enter 5 in the feet field and 7 in the inches field for 5 feet 7 inches. Never enter a decimal value in a form field labeled "feet" unless the form label explicitly says "decimal feet."

Medical and Fitness Use

Medical records in the US use fraction height. Electronic Health Record (EHR) systems like Epic and Cerner store height as total inches internally (67 in for 5'7") and display it as feet and inches. Body Mass Index (BMI) calculators accept height in feet and inches or centimeters. Enter fraction height on all health and fitness platforms unless the app shows a decimal feet field.

International and European medical forms use centimeters. Convert fraction height to centimeters using the formula: total inches × 2.54. For 5'7": 67 in × 2.54 = 170.18 cm.

Everyday Use

Use fraction height in everyday conversation and writing in the US. Write 5'7" in sports profiles, social media bios, and casual measurement references. Use 5 ft 7 in in formal written documents that follow the Associated Press (AP) Stylebook or similar editorial standards. Decimal feet (5.5833 ft) has no everyday use outside of construction and engineering.

Real-World Examples

5'5" vs 5.5 ft

5'5" is 5 feet 5 inches (165.1 cm or 1.651 m). 5.5 ft is 5 feet 6 inches (167.64 cm or 1.6764 m). The difference is 1 inch (2.54 cm). 5.5 ft happens to be a round decimal, so people assume it means 5'5" — but it does not. 5 + (0.5 × 12) = 5 feet 6 inches.

5'10" vs 5.83 ft

5'10" is 5 feet 10 inches (177.8 cm or 1.778 m). The correct decimal representation is 5.8333 ft, not 5.83 ft. Rounding to 5.83 ft gives 5 feet 9.96 inches — a 0.04-inch loss. For human height, this is negligible. For a ceiling height in a construction plan, 0.04 inches repeated across framing members accumulates.

6'0" vs 6.0 ft

6'0" and 6.0 ft are the same value. 6 feet 0 inches in decimal feet is exactly 6.0000 ft. This is the one case where the decimal and fraction values match. 6.0 ft = 6 + (0 × 12) = 6 ft 0 in = 182.88 cm (1.8288 m).

Frequently Asked Questions

Is 5.7 feet the same as 5'7"?

No, 5.7 feet is not the same as 5'7". 5.7 ft equals 5 feet 8.4 inches (173.74 cm) and 5'7" equals 5 feet 7 inches (170.18 cm). The difference is 1.4 inches (3.56 cm).

Why do people confuse decimal and fraction height?

People confuse decimal and fraction height because the numbers look similar. 5.7 resembles 5'7", but the decimal 0.7 represents 0.7 of a foot (8.4 inches), not 7 inches. The decimal system treats height as one continuous value in feet, while fraction notation uses separate feet and inch counts.

Which format is more accurate for height?

Decimal feet are more mathematically precise, supporting any number of decimal places. Fraction height in feet and inches is accurate to the nearest whole inch (±2.54 cm), which is sufficient for human height. For medical records and construction, decimal centimeters (170.18 cm) offer the most practical precision.

Can I convert feet and inches into decimals?

Yes, convert feet and inches to decimal feet by dividing the inches by 12 and adding to the feet value. For 5 feet 7 inches: 7 ÷ 12 = 0.5833, so 5 + 0.5833 = 5.5833 decimal feet. To get total decimal inches: (5 × 12) + 7 = 67 in.

What is the correct way to write height?

The correct way to write height depends on context. Use 5'7" or 5 ft 7 in for US everyday and official use. Use 170 cm or 1.70 m for international and medical contexts. Use decimal feet (5.5833 ft) only in construction, engineering, or CAD software. Never use 5.7 as shorthand for 5'7" — the values are different.

Can height have decimals?

Yes, height can be expressed as a decimal number in feet (5.75 ft) or decimal inches (69.0 in) or decimal centimeters (175.26 cm). Decimal height in feet is standard in CAD software, engineering calculations, and construction databases. Decimal centimeters are the standard in international medical records. Whole-inch fraction height (5'9") is the standard in US everyday and clinical use.

How do I convert decimal height to inches?

To convert decimal feet to total inches, multiply the decimal feet value by 12. For 5.75 ft: 5.75 × 12 = 69 inches. To convert decimal feet to feet and inches, take the integer part as feet and multiply the decimal part by 12 for inches. For 5.75 ft: feet = 5, inches = 0.75 × 12 = 9, so 5 feet 9 inches (5'9" / 175.26 cm / 1.7526 m).

Decimal Height vs Fraction Height: Summary

Decimal height and fraction height describe the same physical measurement in 2 different number formats. Decimal height (5.5833 ft) uses one continuous number in feet. Fraction height (5'7") uses feet and whole inches as 2 separate values. The formats require conversion — they are not interchangeable by reading the digits directly.

For any height conversion, use the formulas above or the tools below to get the exact equivalent without rounding errors.

Use Our Height Conversion Tools

Convert between decimal height, fraction height, centimeters, and total inches with the tools below.