It is a big question! And one that is difficult to answer too. When you see one mouse, you might well assume that you have more… and you might be right! Even if you see one mouse, you need to get rid of the mouse quickly! If you see one mouse how many do you have? Let’s take a look

If I told you that 1 mouse can turn into 127 mice within 147 days, would that concern you? Read this article to find out more.

The good news is if this is the first time you have seen a mouse in your home, then it likely to have only just found a way in. This is good news because it means it has not had time to build a nest and give birth to a litter.

You might be lucky here, but you will still need to investigate further.

Recommended reading: Hunting down common points of entry for mice. Vital for keeping them out of your house, and winning the rodent war!

How Long Has The Mouse Been In My House?

one mouse

In order to find out how many mice you have in your home, this is one of the most important questions to answer.

There are a few things you can do to find out how long you have had a mouse in the house.

The odds are that if you have not seen any evidence of mice activity, and you have only seen 1 mouse, then you may have got lucky!

My best advice is to follow some fool-proof mice control tips to ensure they do not keep getting in your home! Getting rid of mice is a challenge, stopping them from getting in is much easier. This is pest control 101!

Has The Mouse Built A Nest?

It is important to hunt throughout your home for nests.

If you are unable to find a mouse nest in your home, that is awesome news! It means it has not been in your home long enough to create one.

What Is The Average Litter Size For A Mouse?

The average litter size for a mouse is 6-8.

Why is it important to know the average litter size?

It is important to know because if you think you have more than 1 mouse in your home, and you think they may have set up a nest, then you know how many more mice are likely to be in your home.

There is more bad news too! A female reaches sexual maturity at around 6 weeks old. If you have had mice in for longer than 6 weeks, it is possible that you have a mouse infestation on your hands! Time to get out the mouse traps and peanut butter (for bait)…

So, If You See One Mouse How Many Do You Have?

one mouse on ground

The fact that you are asking the question now means that you are unlikely to have seen mouse activity before now.

That is good news!

It is good news because it means you have probably caught your mouse problem before they set up home in your house.

The longer you leave the mouse problem, the more chance you have of allowing a family of mice to expand and destroy your home!

If you have noticed mouse activity in your home before and you are only just asking this question, then we should take the average litter size as the answer, plus 1 (female mouse). The answer is 8.

In short:

  • If seeing a mouse is the first time you have notice mouse activity in your home, it is likely to only be 1 mouse.
  • If you have noticed signs recently, but have ignored them or not realized they are signs, I would suggest the answer is 8.
  • As time goes by, the mouse population in your home explodes and it is not possible to count how many.

You will need to check around your home for mouse activity. This is best completed during the day (mice are nocturnal).

Check throughout your house for:

  • Mouse droppings
  • Urine
  • Evidence of nesting
  • Gnawed items

The ore of these items you see, the more chance there is that you have more than one mouse in your house.

1 Mouse Turns Into Many Mice VERY Quickly!

1 to 127 Mice In 147 Days Infographic

If you have been through the questions on this post and have concluded that you only have 1 mouse, it is awesome news, congrats!

I want to run you through some math to show you how quickly 1 mouse can turn into a house full… first, we need to make an assumption. You have 1 in your home, and it is a pregnant mouse looking for somewhere to nest.

Day 1: 1 mouse

A female mouse is pregnant for around 21 days. The average litter size for a mouse is 6-8. Let’s assume this litter is 6.

Day 21: 7 mice (4 females, 3 males)

A female mouse reaches sexual maturity in 6 weeks. In 6 weeks, you may have 4 pregnant mice in your home.

Day 84: The 4 pregnant mice have given birth. Assuming that the 4 pregnant mice give birth to 6 mice each, you will now have 31 mice in your home. The initial mouse + 6 + 24 (new litters). If we break it down by gender, you now have 16 females and 15 males (on average).

Time for a reminder: in 6 weeks, all of the female mice will reach sexual maturity.

Day 147: All of the female mice have given birth. That is 16 female mice who have given birth to an average of 6 mice per litter. 16 x 6 = 96 mice. Add that to the previous number of mice and you now have 127 mice in your home.

1 mouse to 127 mice can only take 147 days!

I could continue, but I think you get the picture. The message is clear, even if you only have 1 mouse in your home, you should be declaring an all-out war to get rid of it!

Is there ever just one mouse?

If you catch it as soon as it enters your home, then it is very likely to only be one mouse in your home. If you have been hearing noises for some time, there are likely to be more!

You should react immediately when you hear mice noises, and seal up those entry points.

Ultimately, the answer depends entirely on the amount of time the mouse has been in your home. If it has been in your house for more than 6 weeks, you could easily have a mouse infestation on your hands. If you have only found 1 mouse, and that is now gone, you should continue to look for further evidence of activity.

Check everywhere! Check all the places mice like to hide in your home.

Do mice leave on their own?

Mice have been known to leave on their own, yes.

It all depends on what you have on offer. If you allow easy access to:

  • Food
  • Warmth
  • Comfort
  • Protection

…then the mice will definitely not leave! If anything, you are risking an infestation.

The only time I have known mice to leave without any form of pest control is when all the attractions are removed from the property. If they don’t have anything to eat, they will leave in search of food. If they do not feel safe, they will seek another area to set up a nest. For instance, if you have a cat in your home, the mice will be very fearful! The presence of any predator will make mice fearful of settling down in that area.

Also, just because you are lucky enough to have a mouse that has left on its own, it doesn’t mean that it will not be back, and it doesn’t mean that no other mice will find their way in! You must spend some time investigating any potential entry points around your home. This is the best form of rodent control, take it from me!

I have a monthly task in my diary to check around my house for points of entry. If I find any, they are sealed up immediately! Prevention is better than a cure, right?

Frequently Asked Questions

What are mice scared of?

Mice are scared of cats, humans, and noise… pretty much anything that is bigger than they are! You can use this knowledge in your battle to get rid of the mice in your home.

Does one mouse mean an infestation?

Not necessarily, no.

One mouse might just be one mouse… you might be lucky!
Having said that, there is also a very good chance that you have more mice, which can be considered an infestation. You need to check to see how many mice you are dealing with by following the advice on this page. Always ensure that you record any evidence of mice activity because you will need that info to increase your confidence that all the mice have gone and you are totally rodent free!


If you see one mouse how many do you have? After reading this article, you are now in a much better place to be able to answer that question!

What concerned me most of all when writing this article was the math to figure out how quickly 1 mouse can turn into 147 mice in 127 days. I am not going to lie, that sent a few shivers down my spine! Imagine taking that many mice one… your home will be destroyed!

If you notice 1 mouse enter your home, get rid of it quickly.

It is important to remember that mice and mice feces can transmit some nasty diseases. Mouse droppings can be dangerous!

With that in mind, it is vital to ensure that you follow an excellent pest control guide to get rid of mice. Stop them from getting in, and you are winning the war!

Good luck!

About the Author

Rodent Guide

Man v Rodent! I've been tackling Rodent infestation issues for over 20 years. Now I want to use this website to pass over the tips that I have learned over that time to help you take these Rodents out DIY style!

View All Articles