Measuring a moldboard plow comes down to one key number: the width of the bottom, measured in inches across the cutting edge. This single measurement tells you the plow’s size, determines which replacement parts fit, and defines how wide a furrow it cuts. But getting an accurate picture of your plow requires a few different measurements depending on whether you’re sizing bottoms, matching parts to a frame, or setting up for proper depth and clearance.
Measuring the Bottom Width
The bottom width is the defining measurement of any moldboard plow. It refers to the distance from the wing of the share (the outer cutting edge) to the landside, measured perpendicular to the direction of travel. Common sizes range from 10 inches on smaller plows up to 18 inches on heavy-duty models, with 12, 14, and 16 inches being the most typical.
To take this measurement, lay a tape measure across the share at its widest point, from the outermost tip of the wing straight across to the landside edge. This tells you the width of furrow the plow is designed to cut. If you’re buying replacement shares or moldboards, this is the number you need.
Measuring the Frame Width
If you’re trying to identify an unmarked or vintage plow, or figure out what size bottoms it accepts, you’ll want to measure the frame. Measure across the beams at the top of the plow, either edge to edge or center to center. The parallel distance between the beams tells you what size bottoms the frame was built to carry.
Not all frames are fixed to one size. Some manufacturers, particularly International Harvester, built adjustable-width frames. A smaller two-bottom frame might adjust to accept 10, 11, 12, or 14-inch bottoms, while a larger two-bottom frame could handle 12, 14, or 16-inch bottoms. Three and four-bottom plows follow similar patterns, and most plows larger than four bottoms are typically set up for 16-inch or 18-inch bottoms only.
The important thing to understand is that a bottom designed for one width range won’t necessarily work at every frame setting. A 12-inch bottom, for example, won’t function properly if you spread the frame to a 16-inch setting. There are roughly four different bottom sizes that cover the full range from 10 to 18 inches, so matching the right bottom to the right frame setting matters for both cut quality and safety.
Measuring Vertical Clearance
Vertical clearance tells you how much space exists between the cutting edge of the share and the nearest part of the frame above it, whether that’s the main beam, a truss, or a trip mechanism. This measurement determines how well the plow handles crop residue, roots, and other debris without clogging.
To measure it, place one end of a tape measure or straight edge at the cutting edge of the share, then measure straight up to the lowest overhead obstruction. More clearance means the plow can roll heavier trash through without jamming. If you’re plowing fields with significant residue, this number matters more than you might expect. Plows designed for heavy residue conditions will have noticeably more vertical clearance than lighter-duty models.
Measuring Depth Capability
Plowing depth is set by your tractor’s three-point hitch or hydraulic controls, but the plow itself has a maximum working depth determined by the height of the moldboard. Measure from the bottom of the share point straight up along the face of the moldboard to its top edge. This gives you the deepest the plow can reasonably turn a furrow without soil spilling over the top of the board instead of being fully inverted.
Most standard moldboard plows work in the 6 to 12-inch depth range. If you’re measuring depth in the field, push a ruler or stick into the furrow wall straight down to the furrow bottom. The distance from the original soil surface to the bottom of the cut is your actual working depth.
Measuring for Replacement Parts
When you need new shares, moldboards, or landsides, three measurements will get you to the right part. First, bottom width as described above. Second, measure the length of the share from its point (the forward tip) to its rear mounting bolt holes. Third, note the bolt hole spacing and pattern on both the share and the moldboard, since these vary across manufacturers and even across models from the same brand.
For the moldboard itself, measure its height (bottom edge to top edge) and its length along the curve from front to rear mounting points. Taking these measurements to a parts supplier, along with any model numbers stamped into the frame or frog, will help you get an exact match. If the plow has no visible markings, the combination of bottom width, frame beam spacing, and bolt patterns is usually enough for an experienced dealer to identify the manufacturer and series.
Calculating Total Cut Width
On a multi-bottom plow, the total cut width is simply the bottom width multiplied by the number of bottoms. A three-bottom plow with 14-inch bottoms cuts a 42-inch swath per pass. This number is what you need when estimating field coverage rates or matching the plow to your tractor’s horsepower. A common rule of thumb is that each inch of plow width requires about 1 to 1.5 horsepower at the drawbar, depending on soil type. A three-bottom 14-inch plow (42 inches total) needs roughly 42 to 63 horsepower to pull effectively in average conditions.