Enter your observations
Use measurements you can verify. Unknown or unreadable details can be left unspecified where the tool allows it.
Lock opening
Candidate key
Ready when you are
Your results will appear here without reloading this page.
How to use this tool
- Measure the keyhole opening at its narrowest relevant points without inserting tools that can damage the lock.
- Record the profile shape and lock type only when you can observe them.
- Enter the candidate key’s shank, bit and total dimensions from a ruler or catalogue.
- Review basic conflicts, then verify internal warding and turning clearance with a knowledgeable locksmith.
What the result means
A key needs to pass through the keyhole and align with the lock’s internal geometry. Shank dimensions, bit width/height, keyhole profile and overall length offer useful screening information, but old locks may contain wards, offsets or wear not visible from the outside.
The tool marks elementary width/profile compatibility and deliberately does not claim a working key match. The key’s bitting, blade shape, rotation arc and lock condition may be more important than a small difference in overall length.
Limits and good practice
Do not force a key, turn it against resistance, or enlarge an original keyhole. Keyhole geometry alone does not show internal warding. If an antique lock is valuable or fragile, have a locksmith familiar with historic mechanisms examine it.
References and further research
Frequently asked questions
If the key fits through the hole, will it work?
Not necessarily. The bit profile and internal wards must align, and the lock must be in working condition.
Should I use the key as a measuring tool?
Avoid forcing it into the lock. Measure the keyhole opening and existing key externally whenever possible.
Why does bit height matter?
Bit height contributes to the key’s profile, but only the internal lock arrangement can confirm whether it clears the wards.
Does total key length determine compatibility?
Length is useful for comparison and access, but it does not prove the key will engage or turn the mechanism.
Can this identify the exact lock type?
No. It records broad categories only. Detailed lock identification may require examination of the case and internal parts.
What should I do if the key binds?
Stop rather than force it. Old keys, wards and lock components can bend or break; seek a specialist locksmith.