Swift Academy · Lesson

Floating-Point: Double vs Float

Choose between Double and Float and handle precision.

Lesson 2 of 413 steps

Floating-Point: Double vs Float is a free Swift Academy lesson on CoddyKit. This is lesson 2 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, and your progress syncs across the web and the CoddyKit app. The Swift Academy course includes 4 lessons in total.

Floating-Point Types

Swift has two main floating-point types: Double (64-bit) and Float (32-bit). They represent numbers with fractional parts.

let d: Double = 3.14159
let f: Float = 3.14159
print(d, f)

Double Is the Default

When you write a decimal literal without a type annotation, Swift infers Double. Double offers more precision than Float.

let value = 2.5
print(type(of: value))

Precision Difference

Double stores about 15 significant decimal digits; Float only about 6 or 7. The same literal can print differently.

let d: Double = 0.1234567890123456
let f: Float = 0.1234567890123456
print(d)
print(f)

The pi Constant

Both types provide .pi. Double.pi is more precise than Float.pi.

print(Double.pi)
print(Float.pi)

Floating-Point Arithmetic

You can add, subtract, multiply, and divide floating-point numbers. Division keeps the fractional result.

let radius = 2.0
let area = Double.pi * radius * radius
print("Area:", area)

Rounding Methods

Floating-point values offer .rounded(), plus variants like .rounded(.down) and .rounded(.up).

let x = 2.7
print(x.rounded())
print(x.rounded(.down))
print(x.rounded(.up))

Floor, Ceil, and Truncation

Rounding rules let you floor toward negative infinity, ceil toward positive infinity, or truncate toward zero.

let n = -2.3
print(n.rounded(.down))
print(n.rounded(.up))
print(n.rounded(.towardZero))

Floating-Point Imprecision

Because of binary representation, some decimals cannot be stored exactly. 0.1 + 0.2 is famously not exactly 0.3.

let sum = 0.1 + 0.2
print(sum)
print(sum == 0.3)

Comparing Floats Safely

Instead of exact equality, compare floating-point numbers within a small tolerance (epsilon).

let sum = 0.1 + 0.2
let close = abs(sum - 0.3) < 0.0001
print("Close enough:", close)

Special Float Values

Floating-point types can represent infinity and nan (not a number). Check with .isInfinite and .isNaN.

let inf = Double.infinity
let notNum = Double.nan
print(inf.isInfinite)
print(notNum.isNaN)

Choosing Double or Float

Prefer Double for accuracy in general math. Use Float only when memory or specific hardware (like graphics) demands a 32-bit value.

let preciseAvg: Double = (10.0 + 3.0) / 4.0
print(preciseAvg)

Quick Check

Recall which type Swift infers for decimal literals.

Answer it in the interactive lesson

Recap: Double vs Float

You learned that Double (64-bit, the default) is more precise than Float (32-bit), that both offer .pi and rounding methods, and that floating-point math is imprecise so you should compare with a tolerance rather than ==.

let a = 0.1 + 0.2
print("Raw:", a)
print("Rounded:", a.rounded())
print("Within tolerance of 0.3:", abs(a - 0.3) < 1e-9)

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Frequently Asked Questions

Is the “Floating-Point: Double vs Float” lesson free?

Yes — any 3 lessons of the Swift Academy learning path, including “Floating-Point: Double vs Float”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Swift Academy course includes 4 lessons in total.

What will I learn in “Floating-Point: Double vs Float”?

Choose between Double and Float and handle precision. You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Swift Academy?

No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.

How long does the “Floating-Point: Double vs Float” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Swift Academy lesson?

Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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