Online RulerWhy measuring starts at zero
Start at zero so the reading at the far end gives the object's length directly. A ruler tells you how far a mark is from zero. If the object starts at a different mark, subtract the starting reading from the ending reading to get the length.
- The zero line may sit a little inward from the physical edge of a ruler.
- The first numbered mark you see may be farther along the scale than zero.
- A reading at the far end gives the length directly only when the near end lines up with zero.
- Choose centimeters or inches and find the zero line on that scale. Follow the same row of marks from start to finish.
- Place the ruler beside the object. Turn it until the scale runs parallel to the length you want to measure.
- Line up the near end with zero. Look straight down over that end to check the alignment before you read the other end.
- Look straight down over the far end and read the mark it reaches. If the edge falls between marks, record a range or label your reading as an estimate.
Find the zero line
Check the space before the first printed number. A ruler may have a blank margin before the scale begins. A worn or chipped end can also leave the edge in a different place from the original zero. Use the line where the scale begins, even when the numeral is faint. If you cannot identify that line, pick a clear numbered mark farther along.
Start at another mark
Set the near end on a clear mark and write down its reading. Read the far end on the same scale. Subtract the near reading from the far reading, keeping both in the same unit. This works because the two readings share a starting point. If you see the far reading by itself later, you will need the near reading to recover the length.
Start at zero on screen
On the AR Ruler website and desktop ruler, zero is fixed at the left end. Set the screen scale with the card calibration before you measure. Check the scale again if you change browser zoom or move to another display. Hold the object still with its near end at zero and move the marker to the far end.
Can I use the ruler's edge?
Yes, if the zero line meets that edge. Check where the scale actually begins before lining up the object.
What if the end is rounded?
Use the outermost point in the direction you are measuring. A straight piece of paper held square to the ruler can help you line up that point.
Should I move the ruler or the object?
Move whichever is easier to control. Once zero and the near end line up, hold both steady while you read the far end.