How to Measure a Manhole Cover (The Right Way)

Getting the right size is essential to ensure your manhole cover fits correctly - whether you’re replacing an old one or fitting new.

One of the most common questions we get at Eco Trade Counter is:
“Which part of the manhole do I actually measure?”

Here’s a straightforward guide to help you measure accurately and buy with confidence.

Step 1: Don’t Measure the Lid

A common mistake is measuring the lid itself.
Manhole covers are not sized by the lid - they’re sized by the hole they cover.

What you need is the clear opening size.
This means the internal width, length, or diameter of the chamber (the space between the inside edges of the hole).

Also known as:

• Clear internal opening

• Chamber opening

• Structural opening

Step 2: Remove the Lid (If Possible)

To get an accurate measurement:

1. Lift the existing lid carefully using the right lifting keys or tools.

2. Measure the internal width and length (for square or rectangular) or internal diameter (for round).

3. Record these in millimetres (mm) - this is the standard used for manhole covers.

This is the size you should use when buying a new manhole cover from Eco Trade Counter.

If You Can’t Remove the Lid

You can still make a close estimate:

1. Measure the overall size of the cover (edge to edge).

2. Subtract around 50–100mm from both the width and length.

Example:
If your existing cover measures 670 x 530mm, you’ll likely need one with a 600 x 450mm clear opening.

Why the Clear Opening Matters

Choosing the correct clear opening size ensures the cover fits properly and safely.
Measuring the lid instead can result in a poor fit, risking movement or damage over time.

Measuring by Shape

Round Manholes
Measure the internal diameter.
You can use a square cover with an opening large enough - usually 300mm or 450mm.

Rectangular Manholes
Measure the internal width and length.

Remember:

• Clear opening size is what you need.

• Overall size is what you may have to use if the lid can’t be removed.

What About Recessed Manhole Covers?

The same measurement applies - recessed covers are still sized by the clear opening, not by tray depth.

Choose the right recess depth for your finish:

• Tiles: 20–45mm

• Block paving: 80–100mm

For indoor or sealed installations, consider a sealed or locking cover.
The Alusthetic triple-sealed range is ideal for internal or odour-tight applications.

Ready to Buy?

Once you’ve taken your measurements, you’re ready to order.
Each listing on Eco Trade Counter clearly shows the clear opening size - just match it to your measurement.

Shop Manhole Covers at Eco Trade Counter

Visual Guide

Quick Measuring Checklist

• Don’t measure the lid

• Measure the internal clear opening

• Record in millimetres (mm)

• Round cover? Measure diameter

• Rectangular cover? Measure width × length

• Lid stuck? Subtract 50–100mm from overall size

• Always buy by clear opening size