To measure a plow bottom, you measure the width of the furrow it cuts, not any single part. Standing behind the plow, measure the distance from the landside to the outer lower edge of the plow share. That measurement, typically given in inches (10″, 12″, 14″, 16″), tells you the size of your plow bottom.
Where to Measure on a Single Bottom
The plow share is the cutting piece at the front of the bottom, with a rounded point that sits on top of the landside. The landside is the flat piece that runs along the ground on the furrow wall side of the plow, extending behind the bottom. These two parts define the boundaries of your measurement.
Position yourself behind the plow and find the landside. Then locate the outside lower edge of the share, the side farthest from the landside. Measure straight across between those two points. You’re not measuring the length of the share or the height of the moldboard. You’re measuring the horizontal width of earth the bottom will slice and turn. A measurement of 14 inches means you have a 14-inch plow bottom, and each pass will cut a 14-inch furrow.
Measuring a Multi-Bottom Plow
If your plow has two or more bottoms mounted on a common frame, there’s an even simpler method. Measure the spacing between adjacent beams (the structural members that hold each bottom to the frame), going directly crosswise and center to center. That beam-to-beam distance equals the width of each bottom.
This works because the bottoms on a gang plow are spaced so each one cuts a furrow exactly as wide as its rated size, with no overlap and no uncut strip between them. So a two-bottom plow with 16 inches between beam centers is a 2×16″ plow, cutting a total of 32 inches per pass.
Common Plow Bottom Sizes
Plow bottoms generally come in standard sizes measured in two-inch increments. Here are the most common:
- 10″ and 12″: Small bottoms found on single-bottom or light two-bottom plows, suited to garden tractors and compact utility tractors.
- 14″: One of the most popular sizes for older and mid-sized farm tractors. Many vintage two- and three-bottom plows use 14-inch bottoms.
- 16″: Common on mid-range to larger row-crop tractors. A three-bottom 16″ plow cuts a 48-inch swath.
- 18″ and 20″: Larger bottoms that require significantly more horsepower per bottom, typically found on higher-horsepower tractors.
Why the Size Matters
Knowing your plow bottom size is essential for two practical reasons. First, it tells you how much horsepower you need. A common rule of thumb is roughly 1 to 1.5 engine horsepower per inch of total cut width, depending on soil type. A three-bottom 14″ plow (42 inches total) needs a tractor in the 42 to 63 horsepower range under normal conditions. Heavy clay or rocky ground pushes that number higher.
Second, the measurement determines which replacement shares and moldboards fit your plow. Shares are wear items that need regular replacement, and they’re sized to the bottom. A 14-inch share won’t fit a 16-inch bottom. When ordering parts, you’ll need both the bottom size and the plow manufacturer and model, since share bolt patterns and mounting styles vary between brands even at the same width.
Tips for an Accurate Measurement
If the share is heavily worn, the outer edge may have lost material, which can make your measurement come up short. Compare your number against the beam spacing method if you have a multi-bottom plow, or look for a size stamp on the share or frog (the casting the share bolts to). Many manufacturers stamped the bottom size directly into the frog or onto a tag on the beam.
Measure with the plow on flat ground and the share sitting in its working position. If the plow is raised and angled, you can introduce error. A simple tape measure is all you need, and rounding to the nearest even inch will land you on the correct standard size.