Multiplying large numbers by a one-digit number
In 4th grade, children learn to multiply a number of up to four digits by a one-digit number, such as 3,045 × 8, by breaking the larger number apart by place value.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 4th grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
Beads come in bags of 125. Jamal buys 6 bags to make bracelets. How many beads does he get?
- 620
- 750
- 625
Why this matters
Multiplying a big number by a small one gives your child a quick way to answer real questions, like how many pages are in 4 books of 312 pages each. It leads to multiplying two two-digit numbers and dividing larger numbers this year, and in 5th grade to the stacked written method and multiplying decimals. And it shows up whenever an amount repeats: a weekly total over several weeks, or the cost of a few of the same thing.
Later comes multiplying two two-digit numbers, which breaks apart both numbers instead of one.
Where kids can get stuck
- Writing each digit’s product side by side, so 48 × 7 becomes 2,856 instead of 336.
- Losing track of the zero in a number like 3,045, multiplying the 3 as 300 and getting 2,760 instead of 24,360.
- Adding the leftover digits instead of multiplying them, so 427 × 6 becomes 2,400 + 27 = 2,427 instead of 2,562.
How you can help
- Ask a question in the car: if a full tank takes you about 315 miles, how far could you go on 4 tanks? Have your child split it as 4 × 300, 4 × 10, and 4 × 5, then add 1,200, 40, and 20.
- Count the steps along one block on a walk, then ask how many steps 6 blocks would be. If one block is 215 steps, that is 6 × 200, 6 × 10, and 6 × 5, or 1,290.
- Work out at bedtime about how many days old your child is. Multiply 365 by their age, such as 365 × 9 = 3,285, then talk about why leap years add a couple more days.
If it’s helpful, you can sign up for free, adaptive practice in Bobby's Math Club.
Questions parents ask
Why does my child write some of these down instead of working them out in their head?
Some can be done in their head: for 4 × 225, your child can think 800 and 100, so 900. But for 3,045 × 8, writing down 24,000, 320, and 40 keeps the pieces from getting lost before adding them to 24,360. Either way, each piece uses a times fact they already know.
What should my child know before multiplying larger numbers?
Times tables up to 10 × 10 help a lot, since every piece is built from them. Your child also needs to multiply by tens, hundreds, and thousands with understanding, such as knowing 40 × 7 = 280 because it is 4 tens times 7. If those feel shaky, a few short, relaxed practice sessions on them can make the bigger problems feel much more manageable.
How can my child check a big multiplication answer?
A quick estimate catches many slips. For 1,987 × 4, your child can round 1,987 to 2,000 and see that the answer should be close to 8,000. The exact answer, 7,948, is a little less, which makes sense because 1,987 is a little less than 2,000. An answer like 4,948 or 79,480 would stand out as wrong right away.
Make learning math fun
Bobby's Math Club turns 4th grade math practice into something fun to do together.
- Unlimited practice, completely free
- Practice that starts where your child is and grows with them
- You see their progress and what to work on next
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Ready to watch your child’s confidence grow?
Your 4th grade child can start today with free, unlimited practice that grows with them.
Join the clubNote for teachers: This skill is covered by Common Core math standard 4.NBT.B.5: “Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.” Learn how Bobby's Math Club can help your students grow. (Common Core 4.NBT.5)