Guide · Identifying and measuring
How to measure a lawn mower blade
Measure blade length diagonally, name the center hole, record width and thickness, then match the maker's record. With Oregon's published examples.
Short answer
Measure the blade's length diagonally, from one tip to the opposite tip, not straight end to end. Then name the center hole: round holes by their inner diameter, star and bow-tie holes by their shape. Add the width and thickness, and compare every figure with the maker's own record for the part before you order.
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Length: measure on the diagonal
USA Mower Blades tells buyers to measure blade length diagonally from one tip to the opposite tip, and warns that a straight end-to-end measurement gives the wrong length.[2] Oregon uses the same convention: its product pages say the length is measured diagonally from the corners of the blade.[3]
So a blade listed at 17-1/16 in is 17-1/16 in corner to corner. Your ruler laid along the blade's center line will read short.
The center hole: measured or named
The center hole is what locks the blade to the spindle or blade adapter, so it matters as much as length. USA Mower Blades describes three cases:[2]
- Round holes are measured by their inner diameter (the center-hole diameter).
- Rounded-rectangle holes are measured by inner length and height.
- Star and H-pattern (bow-tie) holes are identified by name, not by a measurement.
Oregon's Blades by Length catalog records holes as round sizes, 5-point star, 7-point star, "Y, 6 pt. star" and bow-tie, and every name sits in a record for one part number.[4] A hole name alone does not establish fit. Our center-hole shapes guide and the center-hole identifier walk through each shape: round, 5-point star, 6-point star, 7-point star, bow-tie and S-shape.
What a full blade record holds
Length is one field among many. Oregon's catalog records each blade's length, center hole, outer hole, center-to-center spacing, width, thickness, offset, air lift and an L-cut flag.[4] Its online blade catalog also lets shoppers filter by left- or right-hand cut, blade length and center-hole size.[5]
In plain terms:
- Width is how wide the blade bar is.
- Thickness is the steel's thickness.
- Offset is how far the blade steps up or down from its mounting face.
- Air lift is the height of the raised back edge, the "wing".
- Cut direction is whether the blade is made for a spindle turning one way or the other.
Write down every one you can read from your old blade, then match the full set against the maker's record.
Maker-published examples
These are figures each maker publishes for one part number. They are examples of what a record looks like, not sizes for your mower.
| Part | Length | Center hole | Width | Thickness | Other fields |
|---|---|---|---|---|---|
| Oregon 92-105 | 17-1/16 in | 7-point star | 2.75 in | 0.164 in | |
| Oregon 96-347 (Gator G3) | 21 in | 5/8 in | 2.50 in | 0.203 in | zero offset, 3/4 in air lift |
| Oregon 91-635 (Gator G3) | 21-1/8 in | 3/4 in | 0.187 in | 1/4 in offset | |
| Oregon Gator G6 parts | varies by part | varies by part | 3 in | 1/4 in | |
| Oregon 95-601 (Gator G3) | Oregon's pages disagree | 5-point star |
Sources: 92-105[3], 96-347[6], 91-635[7], G6[8], 95-601.[9]
Two blades Oregon calls 21-inch Gator G3 (96-347 and 91-635) differ in hole size, offset and thickness. That is why a length alone never picks a blade. For 95-601 we publish only the 5-point star hole, because Oregon's product page and its catalog give different lengths.
Does thickness matter for fit?
Thickness is part of the maker's record, alongside every other field.[4] Match the record. No maker in our sources publishes a tolerance for "close enough", so do not guess one.
When measuring is not enough
A deck's width does not give you the blade length. Oregon lists its 17-1/16 in 92-105 as used three per 48-inch cut,[3] and its 25-inch 91-544 as used two per 48-inch cut on other decks.[10] Both are 48-inch decks, with very different blades.
A worn or bent blade can also read differently from new. When your measurements and a listing do not agree, go back to the part number: your parts list, your manual or the number stamped on the old blade.
Next
Questions
How do you measure a lawn mower blade?
Measure the length diagonally from one tip to the opposite tip, as USA Mower Blades and Oregon both describe. Then name or measure the center hole, record width and thickness, and compare them with the maker's record.[2][3]
Is a 21-inch mower's blade 21 inches long?
Not necessarily. The blade's own diagonal length is the spec, and only the maker's record for that part gives it. Two Oregon blades sold as 21-inch Gator G3 parts are listed at 21 in and 21-1/8 in, with different holes.[6][7]
How do I measure a star center hole?
You do not measure it; you name it by its points. USA Mower Blades says star and bow-tie holes are identified by name, while round holes are measured by inner diameter.[2]
Does blade thickness matter for fit?
Thickness is one of the fields in Oregon's blade records, next to length, hole, width, offset and air lift. Match the maker's record; no source we use publishes an acceptable tolerance.[4]