Online RulerMeasure a Flat Washer
Measure the outer diameter from rim to rim across the center of the washer. Measure the inner diameter from one inside edge of the hole to the other, also across the center. Lay the washer flat against a calibrated AR Ruler screen and read both spans in the same unit.
- The outer diameter is the full width of the washer. The inner diameter is the width of the opening.
- A line that misses the center reads short, even when both ends touch the correct edges.
- The website and desktop or browser extension rulers show centimeters or fractional inches. The movable marker shows its distance from zero at the left end.
- Clean and dry the washer. Set the screen on a stable surface and place the washer gently against it. Check the scale with a bank card before you start, especially if the browser zoom or display has changed.
- Line up the near outside rim with zero. Look straight at the screen and slide the washer sideways until the ruler passes through the middle of the hole. Move the marker to the far outside rim.
- Keep the ruler across the center of the hole. Use the marker to read both inside edges where the opening meets the metal. Subtract the smaller reading from the larger.
- Turn the washer and check both spans again. Write down the outer and inner readings with their units. If the readings differ by direction, record that difference and note which direction you measured.
Find the center
Use the hole as a visual guide. Move the washer slightly across the ruler and watch the span inside the hole. It gets wider as the ruler approaches the center and narrower as it moves away. For a round washer with a centered hole, the widest part of the opening also puts the ruler through the widest part of the rim.
Pick the edge
A shiny rim can show a bright line beside the actual boundary. Read where the metal ends. Around the hole, a rounded lip can make the opening look wider at the surface. Look straight through the hole and use the visible opening. Keep the washer flat so it cannot tilt as you move the marker.
Check the scale
If you calibrate with the long edge of a standard ISO ID-1 bank card, its nominal width is 85.60 mm. AR Ruler saves the calibration locally. The card serves as a physical reference, and the ruler takes no data from it. Recheck the scale if you change the browser zoom or move the ruler to a different display.
What if the rim is too wide for the screen?
Use a physical ruler or a printed scale that can span the entire washer. Keep zero and the far rim visible in the same setup.
Can I calculate the hole size from the rim?
Read the opening directly. Washers with the same outer diameter can have different hole sizes.
What if an edge lands between ticks?
Record an approximate reading or write down the marks it falls between.