Ordering foam cut to size is one of the easiest ways to upgrade seating, mattresses or cushions — but accurate measuring is critical.
A few millimetres can make the difference between a snug, professional fit and a cushion that bows, wrinkles or won’t sit flat.
This guide explains exactly how to measure foam for bench seats, caravan mattresses, boat berths and custom cushions so you get it right the first time.
Step 1: Measure the Space — Not the Old Foam
If you are replacing existing foam, avoid measuring compressed or sagging inserts.
Instead:
- Remove the foam completely
- Measure the internal cavity of the cover (if reusing it), or
- Measure the actual frame or platform where the foam will sit
Old foam often shrinks, softens or distorts over time. Measuring it can result in a poor fit.
Step 2: Measure Length and Width Accurately
Use a firm tape measure and measure:
- Front to back
- Side to side
- Multiple points across the surface
For built-in seating, measure at the top and bottom of the cavity. Walls and cabinetry are not always perfectly square.
Record measurements in millimetres for best accuracy.
Step 3: Measure the Thickness (Height)
Foam thickness affects both comfort and fit.
Measure:
- The internal depth of the cover (if keeping it)
- The height available within cabinetry
- Clearance for lids or storage access
If reusing a cover, reduce the foam thickness by 5–10mm to allow for easy insertion and zipper closure.
If the foam is going directly into a new cover, we can cut it to exact size.
Step 4: Measuring Irregular Shapes
Many caravan, boat and window seat cushions are not simple rectangles.
Common shapes include:
- Cut corners
- Angled backs
- Trapezoids
- V-berths
- Rounded edges
For irregular shapes, the most accurate method is creating a template.
How to Make a Template
- Lay builder’s paper, cardboard or heavy paper over the space
- Trace the exact shape
- Mark clearly which edge is the front
- Label all dimensions
- Include notes for angles or curves
If possible, send clear photos along with the template or sketch.
Step 5: Measuring Caravan and Boat Mattresses
Caravan and marine layouts often include:
- Island beds with cut corners
- East-west beds
- Bunk mattresses
- V-berths
Measure:
- Total length
- Width at the head and foot (these can differ)
- Depth of any cut corners
- Angle direction
Always confirm which side the cut corner is on when standing at the foot of the bed facing the head.
A quick phone photo alongside your measurements helps avoid confusion.
Step 6: Allowing for Upholstery
If your foam will be upholstered:
- Consider fabric thickness
- Account for piping or boxing
- Confirm whether the cover has stretch or rigid fabric
Tight woven fabrics require slightly more tolerance than stretch fabrics.
If you’re unsure, we can advise based on your chosen fabric and application.
Common Measuring Mistakes to Avoid
- Measuring old compressed foam
- Forgetting to account for fabric thickness
- Rounding measurements too much
- Guessing angles instead of templating
- Not specifying which side is the front
Accuracy ensures a clean, professional finish.
Why Precision Matters
Correct measurements ensure:
- Cushions sit flat
- No bowing or bulging
- Covers zip smoothly
- Edges stay aligned
- Comfort feels consistent
Custom foam should look like it was made for the space — because it was.
Need Help Measuring?
Enviro-Foam specialises in custom foam cut to size for:
- Bench seating
- Window seats
- Caravan mattresses
- Boat cushions
- Replacement lounge inserts
- Irregular and angled shapes
If you’re unsure, send us your measurements, sketch or template and we’ll guide you through it.
Getting the measurements right is the first step to getting the comfort right.