diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index d1307b6db..5bc2f1015 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -18,7 +18,7 @@ use std::rc::Rc;
 use crate::cache::Cache;
 use crate::color::Color;
 use crate::diag::{Diag, DiagSet, Pass};
-use crate::geom::{Angle, Length, Relative};
+use crate::geom::{Angle, Fractional, Length, Relative};
 use crate::loading::{FileHash, Loader};
 use crate::parse::parse;
 use crate::syntax::visit::Visit;
@@ -250,6 +250,7 @@ impl Eval for Expr {
             Self::Length(_, v, unit) => Value::Length(Length::with_unit(v, unit)),
             Self::Angle(_, v, unit) => Value::Angle(Angle::with_unit(v, unit)),
             Self::Percent(_, v) => Value::Relative(Relative::new(v / 100.0)),
+            Self::Fractional(_, v) => Value::Fractional(Fractional::new(v)),
             Self::Color(_, v) => Value::Color(Color::Rgba(v)),
             Self::Str(_, ref v) => Value::Str(v.clone()),
             Self::Ident(ref v) => match ctx.scopes.get(&v) {
diff --git a/src/eval/ops.rs b/src/eval/ops.rs
index 69a0b02b2..15c09e03a 100644
--- a/src/eval/ops.rs
+++ b/src/eval/ops.rs
@@ -11,6 +11,7 @@ pub fn pos(value: Value) -> Value {
         Length(v) => Length(v),
         Angle(v) => Angle(v),
         Relative(v) => Relative(v),
+        Fractional(v) => Fractional(v),
         Linear(v) => Linear(v),
         _ => Error,
     }
@@ -24,6 +25,7 @@ pub fn neg(value: Value) -> Value {
         Length(v) => Length(-v),
         Angle(v) => Angle(-v),
         Relative(v) => Relative(-v),
+        Fractional(v) => Fractional(-v),
         Linear(v) => Linear(-v),
         _ => Error,
     }
@@ -44,6 +46,7 @@ pub fn add(lhs: Value, rhs: Value) -> Value {
         (Relative(a), Length(b)) => Linear(a + b),
         (Relative(a), Relative(b)) => Relative(a + b),
         (Relative(a), Linear(b)) => Linear(a + b),
+        (Fractional(a), Fractional(b)) => Fractional(a + b),
         (Linear(a), Length(b)) => Linear(a + b),
         (Linear(a), Relative(b)) => Linear(a + b),
         (Linear(a), Linear(b)) => Linear(a + b),
@@ -84,6 +87,7 @@ pub fn sub(lhs: Value, rhs: Value) -> Value {
         (Relative(a), Length(b)) => Linear(a - b),
         (Relative(a), Relative(b)) => Relative(a - b),
         (Relative(a), Linear(b)) => Linear(a - b),
+        (Fractional(a), Fractional(b)) => Fractional(a - b),
         (Linear(a), Length(b)) => Linear(a - b),
         (Linear(a), Relative(b)) => Linear(a - b),
         (Linear(a), Linear(b)) => Linear(a - b),
@@ -108,8 +112,13 @@ pub fn mul(lhs: Value, rhs: Value) -> Value {
         (Float(a), Angle(b)) => Angle(a * b),
         (Relative(a), Int(b)) => Relative(a * b as f64),
         (Relative(a), Float(b)) => Relative(a * b),
+        (Fractional(a), Fractional(b)) => Fractional(a * b.get()),
+        (Fractional(a), Int(b)) => Fractional(a * b as f64),
+        (Fractional(a), Float(b)) => Fractional(a * b),
         (Int(a), Relative(b)) => Relative(a as f64 * b),
+        (Int(a), Fractional(b)) => Fractional(a as f64 * b),
         (Float(a), Relative(b)) => Relative(a * b),
+        (Float(a), Fractional(b)) => Fractional(a * b),
         (Linear(a), Int(b)) => Linear(a * b as f64),
         (Linear(a), Float(b)) => Linear(a * b),
         (Int(a), Linear(b)) => Linear(a as f64 * b),
@@ -134,6 +143,9 @@ pub fn div(lhs: Value, rhs: Value) -> Value {
         (Relative(a), Int(b)) => Relative(a / b as f64),
         (Relative(a), Float(b)) => Relative(a / b),
         (Relative(a), Relative(b)) => Float(a / b),
+        (Fractional(a), Fractional(b)) => Float(a.get() / b.get()),
+        (Fractional(a), Int(b)) => Fractional(a / b as f64),
+        (Fractional(a), Float(b)) => Fractional(a / b),
         (Linear(a), Int(b)) => Linear(a / b as f64),
         (Linear(a), Float(b)) => Linear(a / b),
         _ => Error,
diff --git a/src/eval/value.rs b/src/eval/value.rs
index 94f7f5698..498403e69 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -8,7 +8,7 @@ use std::rc::Rc;
 use super::EvalContext;
 use crate::color::{Color, RgbaColor};
 use crate::exec::ExecContext;
-use crate::geom::{Angle, Length, Linear, Relative};
+use crate::geom::{Angle, Fractional, Length, Linear, Relative};
 use crate::syntax::{Expr, Span, Spanned, Tree};
 
 /// A computational value.
@@ -28,6 +28,8 @@ pub enum Value {
     Angle(Angle),
     /// A relative value: `50%`.
     Relative(Relative),
+    /// A fractional value: `1fr`.
+    Fractional(Fractional),
     /// A combination of an absolute length and a relative value: `20% + 5cm`.
     Linear(Linear),
     /// A color value: `#f79143ff`.
@@ -75,6 +77,7 @@ impl Value {
             Self::Length(_) => Length::TYPE_NAME,
             Self::Angle(_) => Angle::TYPE_NAME,
             Self::Relative(_) => Relative::TYPE_NAME,
+            Self::Fractional(_) => Fractional::TYPE_NAME,
             Self::Linear(_) => Linear::TYPE_NAME,
             Self::Color(_) => Color::TYPE_NAME,
             Self::Str(_) => String::TYPE_NAME,
@@ -601,6 +604,7 @@ primitive! {
 primitive! { Length: "length", Value::Length }
 primitive! { Angle: "angle", Value::Angle }
 primitive! { Relative: "relative", Value::Relative }
+primitive! { Fractional: "fractional", Value::Fractional }
 primitive! {
     Linear: "linear",
     Value::Linear,
diff --git a/src/geom/fr.rs b/src/geom/fr.rs
new file mode 100644
index 000000000..974d675ee
--- /dev/null
+++ b/src/geom/fr.rs
@@ -0,0 +1,101 @@
+use decorum::N64;
+
+use super::*;
+
+/// A fractional length.
+#[derive(Default, Copy, Clone, PartialEq, PartialOrd, Hash)]
+pub struct Fractional(N64);
+
+impl Fractional {
+    /// Takes up zero space: `0fr`.
+    pub fn zero() -> Self {
+        Self(N64::from(0.0))
+    }
+
+    /// Takes up as much space as all other items with this fractional size: `1fr`.
+    pub fn one() -> Self {
+        Self(N64::from(1.0))
+    }
+
+    /// Create a new fractional value.
+    pub fn new(ratio: f64) -> Self {
+        Self(N64::from(ratio))
+    }
+
+    /// Get the underlying ratio.
+    pub fn get(self) -> f64 {
+        self.0.into()
+    }
+
+    /// Whether the ratio is zero.
+    pub fn is_zero(self) -> bool {
+        self.0 == 0.0
+    }
+}
+
+impl Display for Fractional {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}fr", self.get())
+    }
+}
+
+impl Debug for Fractional {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        Display::fmt(self, f)
+    }
+}
+
+impl Neg for Fractional {
+    type Output = Self;
+
+    fn neg(self) -> Self {
+        Self(-self.0)
+    }
+}
+
+impl Add for Fractional {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Self(self.0 + other.0)
+    }
+}
+
+sub_impl!(Fractional - Fractional -> Fractional);
+
+impl Mul<f64> for Fractional {
+    type Output = Self;
+
+    fn mul(self, other: f64) -> Self {
+        Self(self.0 * other)
+    }
+}
+
+impl Mul<Fractional> for f64 {
+    type Output = Fractional;
+
+    fn mul(self, other: Fractional) -> Fractional {
+        other * self
+    }
+}
+
+impl Div<f64> for Fractional {
+    type Output = Self;
+
+    fn div(self, other: f64) -> Self {
+        Self(self.0 / other)
+    }
+}
+
+impl Div for Fractional {
+    type Output = f64;
+
+    fn div(self, other: Self) -> f64 {
+        self.get() / other.get()
+    }
+}
+
+assign_impl!(Fractional += Fractional);
+assign_impl!(Fractional -= Fractional);
+assign_impl!(Fractional *= f64);
+assign_impl!(Fractional /= f64);
diff --git a/src/geom/mod.rs b/src/geom/mod.rs
index 0031c6df1..ce8a7276e 100644
--- a/src/geom/mod.rs
+++ b/src/geom/mod.rs
@@ -5,6 +5,7 @@ mod macros;
 mod align;
 mod angle;
 mod dir;
+mod fr;
 mod gen;
 mod length;
 mod linear;
@@ -18,6 +19,7 @@ mod spec;
 pub use align::*;
 pub use angle::*;
 pub use dir::*;
+pub use fr::*;
 pub use gen::*;
 pub use length::*;
 pub use linear::*;
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 048bcb1c5..3d4cc2ac1 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -335,6 +335,7 @@ fn literal(p: &mut Parser) -> Option<Expr> {
         Token::Length(val, unit) => Expr::Length(span, val, unit),
         Token::Angle(val, unit) => Expr::Angle(span, val, unit),
         Token::Percent(p) => Expr::Percent(span, p),
+        Token::Fraction(p) => Expr::Fractional(span, p),
         Token::Color(color) => Expr::Color(span, color),
         Token::Str(token) => Expr::Str(span, {
             if !token.terminated {
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 74051801d..9d3cbc9a2 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -393,6 +393,7 @@ impl<'s> Tokens<'s> {
         // Otherwise parse into the fitting numeric type.
         let build = match suffix {
             "%" => Token::Percent,
+            "fr" => Token::Fraction,
             "pt" => |x| Token::Length(x, LengthUnit::Pt),
             "mm" => |x| Token::Length(x, LengthUnit::Mm),
             "cm" => |x| Token::Length(x, LengthUnit::Cm),
@@ -880,6 +881,7 @@ mod tests {
 
         let suffixes = [
             ("%", Percent as fn(f64) -> Token<'static>),
+            ("fr", Fraction as fn(f64) -> Token<'static>),
             ("mm", |x| Length(x, LengthUnit::Mm)),
             ("pt", |x| Length(x, LengthUnit::Pt)),
             ("cm", |x| Length(x, LengthUnit::Cm)),
diff --git a/src/pretty.rs b/src/pretty.rs
index dc1e284ca..df1d844c1 100644
--- a/src/pretty.rs
+++ b/src/pretty.rs
@@ -4,7 +4,7 @@ use std::fmt::{self, Arguments, Write};
 
 use crate::color::{Color, RgbaColor};
 use crate::eval::*;
-use crate::geom::{Angle, Length, Linear, Relative};
+use crate::geom::{Angle, Fractional, Length, Linear, Relative};
 use crate::syntax::*;
 
 /// Pretty print an item and return the resulting string.
@@ -192,6 +192,7 @@ impl Pretty for Expr {
             Self::Length(_, v, u) => write!(p, "{}{}", v, u).unwrap(),
             Self::Angle(_, v, u) => write!(p, "{}{}", v, u).unwrap(),
             Self::Percent(_, v) => write!(p, "{}%", v).unwrap(),
+            Self::Fractional(_, v) => write!(p, "{}fr", v).unwrap(),
             Self::Color(_, v) => v.pretty(p),
             Self::Str(_, v) => v.pretty(p),
             Self::Ident(v) => v.pretty(p),
@@ -456,6 +457,7 @@ impl Pretty for Value {
             Value::Length(v) => v.pretty(p),
             Value::Angle(v) => v.pretty(p),
             Value::Relative(v) => v.pretty(p),
+            Value::Fractional(v) => v.pretty(p),
             Value::Linear(v) => v.pretty(p),
             Value::Color(v) => v.pretty(p),
             Value::Str(v) => v.pretty(p),
@@ -575,6 +577,7 @@ pretty_display! {
     Length,
     Angle,
     Relative,
+    Fractional,
     Linear,
     RgbaColor,
     Color,
@@ -659,6 +662,7 @@ mod tests {
         roundtrip("{10pt}");
         roundtrip("{14.1deg}");
         roundtrip("{20%}");
+        roundtrip("{0.5fr}");
         roundtrip("{#abcdef}");
         roundtrip(r#"{"hi"}"#);
         test_parse(r#"{"let's \" go"}"#, r#"{"let's \" go"}"#);
@@ -725,6 +729,7 @@ mod tests {
         test_value(Angle::deg(90.0), "90deg");
         test_value(Relative::one() / 2.0, "50%");
         test_value(Relative::new(0.3) + Length::cm(2.0), "30% + 2cm");
+        test_value(Fractional::one() * 7.55, "7.55fr");
         test_value(Color::Rgba(RgbaColor::new(1, 1, 1, 0xff)), "#010101");
         test_value("hello", r#""hello""#);
         test_value("\n", r#""\n""#);
diff --git a/src/syntax/expr.rs b/src/syntax/expr.rs
index e0135d1c3..4dac9c596 100644
--- a/src/syntax/expr.rs
+++ b/src/syntax/expr.rs
@@ -24,6 +24,8 @@ pub enum Expr {
     /// _Note_: `50%` is stored as `50.0` here, but as `0.5` in the
     /// corresponding [value](crate::geom::Relative).
     Percent(Span, f64),
+    /// A fraction unit literal: `1fr`.
+    Fractional(Span, f64),
     /// A color literal: `#ffccee`.
     Color(Span, RgbaColor),
     /// A string literal: `"hello!"`.
@@ -73,6 +75,7 @@ impl Expr {
             Self::Length(span, _, _) => span,
             Self::Angle(span, _, _) => span,
             Self::Percent(span, _) => span,
+            Self::Fractional(span, _) => span,
             Self::Color(span, _) => span,
             Self::Str(span, _) => span,
             Self::Ident(ref v) => v.span,
diff --git a/src/syntax/token.rs b/src/syntax/token.rs
index 9098f1768..56ab3dd6d 100644
--- a/src/syntax/token.rs
+++ b/src/syntax/token.rs
@@ -133,6 +133,8 @@ pub enum Token<'s> {
     /// _Note_: `50%` is stored as `50.0` here, as in the corresponding
     /// [literal](super::Expr::Percent).
     Percent(f64),
+    /// A fraction unit: `3fr`.
+    Fraction(f64),
     /// A color value: `#20d82a`.
     Color(RgbaColor),
     /// A quoted string: `"..."`.
@@ -258,6 +260,7 @@ impl<'s> Token<'s> {
             Self::Length(_, _) => "length",
             Self::Angle(_, _) => "angle",
             Self::Percent(_) => "percentage",
+            Self::Fraction(_) => "`fr` value",
             Self::Color(_) => "color",
             Self::Str(_) => "string",
             Self::LineComment(_) => "line comment",
diff --git a/src/syntax/visit.rs b/src/syntax/visit.rs
index 86481d4e1..ba7555f20 100644
--- a/src/syntax/visit.rs
+++ b/src/syntax/visit.rs
@@ -80,6 +80,7 @@ visit! {
             Expr::Length(_, _, _) => {}
             Expr::Angle(_, _, _) => {}
             Expr::Percent(_, _) => {}
+            Expr::Fractional(_, _) => {}
             Expr::Color(_, _) => {}
             Expr::Str(_, _) => {}
             Expr::Ident(_) => {}
diff --git a/tests/typ/code/ops.typ b/tests/typ/code/ops.typ
index ef249c433..e2ecd4ff0 100644
--- a/tests/typ/code/ops.typ
+++ b/tests/typ/code/ops.typ
@@ -10,7 +10,7 @@
 // Test math operators.
 
 // Test plus and minus.
-#for v in (1, 3.14, 12pt, 45deg, 90%, 13% + 10pt) {
+#for v in (1, 3.14, 12pt, 45deg, 90%, 13% + 10pt, 6.3fr) {
     // Test plus.
     test(+v, v)
 
diff --git a/tools/support/typst.tmLanguage.json b/tools/support/typst.tmLanguage.json
index c7fdcb52d..0b0298fef 100644
--- a/tools/support/typst.tmLanguage.json
+++ b/tools/support/typst.tmLanguage.json
@@ -275,6 +275,10 @@
           "name": "constant.numeric.percentage.typst",
           "match": "\\b(\\d*)?\\.?\\d+([eE][+-]?\\d+)?%"
         },
+        {
+          "name": "constant.numeric.fr.typst",
+          "match": "\\b(\\d*)?\\.?\\d+([eE][+-]?\\d+)?fr"
+        },
         {
           "name": "constant.numeric.integer.typst",
           "match": "\\b\\d+\\b"