What are we calculating?

A rectangle is a four-sided shape with opposite sides equal and all angles 90°. Two measurements fully describe it:

• Length (L)
• Width (W)

From those, we can get four useful results:

1. Area – how much surface the rectangle covers
   Formula: Area = L × W
2. Perimeter – the total distance around the rectangle
   Formula: Perimeter = 2 × (L + W)
3. Diagonal – the line from one corner to the opposite corner
   Uses the Pythagorean theorem:
   Formula: Diagonal = √(L² + W²)
4. Aspect ratio – the shape’s proportions, shown as L:W simplified

How the calculator does it (step by step)

1. You enter Length and Width.
   Decimals are okay. If you type 12.5 or 3.75, it will handle that fine.
2. Pick the units for each side.
   You can keep both in the same unit (like meters) or use different units (like cm for length and m for width). The calculator quietly converts everything to a common base (meters under the hood), so your results stay correct.
3. Choose the result unit for Area.
   Want the area in m², ft², cm², acres, or hectares? Select it, and the calculator converts automatically.
4. Select the number of decimal places.
   If you need neat whole numbers for a quick estimate, choose fewer decimals. If you need precision (DIY cutting, construction, or design), choose more.
5. Click Calculate.
   Instantly, you’ll see the Area, Perimeter, Diagonal, and Aspect ratio, plus a small conversions table that shows the area in multiple units (handy when you’re comparing specs or shopping materials).

Real-world examples (so it sticks)

Example 1: Everything in meters

• Length = 5 m
• Width = 3 m
• Area = 5 × 3 = 15 m²
• Perimeter = 2 × (5 + 3) = 16 m
• Diagonal = √(5² + 3²) = √34 ≈ 5.831 m
• Aspect ratio = 5 : 3 (already simplified)

Example 2: Everything in feet

• Length = 12 ft
• Width = 8 ft
• Area = 12 × 8 = 96 ft²
• Perimeter = 2 × (12 + 8) = 40 ft
• Diagonal = √(12² + 8²) = √208 ≈ 14.422 ft
• Aspect ratio = 12 : 8 → divide both by 4 → 3 : 2

Example 3: Mixed units

• Length = 120 cm
• Width = 2 m
  (Internally: 120 cm = 1.2 m)
• Area = 1.2 × 2 = 2.4 m²
  If you want this in square feet: 2.4 m² × 10.7639 ≈ 25.833 ft²
• Perimeter = 2 × (1.2 + 2) = 6.4 m
• Diagonal = √(1.2² + 2²) = √5.44 ≈ 2.332 m
• Aspect ratio: convert to the same unit first (cm) → 120 : 200 → divide by 40 → 3 : 5

Tips to avoid mistakes

• Use non-negative values. Length and width can be zero (area becomes zero), but they should never be negative.
• Match your real-world use. If your room is measured in feet, enter feet; if your drawing is in centimeters, use cm. Let the calculator handle the conversions.
• Choose sensible precision. Two decimals are great for most situations. If you’re doing precise fabrication, select more.
• Aspect ratio is about shape, not size. 4:3 and 8:6 are the same shape; the ratio just gets simplified.

Why units matter (quick intuition)

• Area units are squared. If you double a side, area doesn’t just double—it scales with the product. That’s why converting between m² and ft² uses a squared conversion (1 m = 3.28084 ft, but 1 m² = 10.7639 ft²).
• Perimeter/diagonal are linear. They scale with your chosen length unit (m, ft, cm), not squared units.

Mini checklist when using the calculator

1. Enter Length and Width.
2. Pick the units for each side (same or different).
3. Choose the Area result unit (m², ft², etc.).
4. Decide decimal places.
5. Click Calculate and read off Area, Perimeter, Diagonal, and Aspect ratio.

That’s it. With just two measurements and a click, you get everything you need to plan flooring, cut materials, size frames, or double-check specs. Simple inputs, reliable outputs—and no manual math headaches.