Build a Punnett square for any cross in seconds, free and with no signup. Pick your cross type, set the parent genotypes, and get the grid, the genotype ratio, and the phenotype ratio right away.
Please choose both parent genotypes.
Genotype ratio
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Phenotype ratio
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What is a Punnett square?
A grid that predicts the genotypes and phenotypes of offspring from two parents, based on the alleles they carry.
Monohybrid vs dihybrid
One trait gives a 2×2 grid with a 3:1 phenotype ratio. Two traits give a 4×4 grid with the classic 9:3:3:1 ratio.
Genotype vs phenotype
Genotype is the gene makeup like Aa. Phenotype is the visible trait, such as brown or blue eyes, that the genes produce.
What You Get with Our Free Punnett Square Calculator
Monohybrid and Dihybrid Crosses
Solve a single trait cross on a clean 2 by 2 grid, or switch to a dihybrid cross and let the tool build the full 4 by 4 square with all sixteen outcomes for you.
Genotype and Phenotype Ratios
Every result gives you both ratios already reduced to their simplest form, so you get the classic 1:2:1 and 3:1 for monohybrid crosses and 9:3:3:1 for dihybrid crosses without counting cells by hand.
Color Coded Grid
The square shades each offspring by zygosity, green for homozygous dominant, yellow for heterozygous, and red for homozygous recessive, so the pattern is obvious at a glance.
Blood Type Inheritance
Pick from the ABO blood type mode to cross parents using the IA, IB, and i alleles. The tool respects codominance and shows the possible blood types of every child.
Incomplete Dominance and Codominance
Switch the inheritance pattern when a heterozygote does not follow the simple dominant rule, like pink flowers from a red and white cross, and the ratios adjust to match.
Custom Allele Letters
Use the letters your class uses. Set your own dominant and recessive symbols and the parent genotype options rebuild around them instantly.
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Built for Students and Teachers Who Want the Math Right
A Punnett square looks simple until a cell goes wrong and the whole ratio falls apart. We built this free tool to take the counting off your hands and give you a result you can check your own work against. The grid, the gametes, and the ratios all follow the same rules your textbook uses, so what you see here is what your teacher expects to see on the page.
It pairs well with the rest of our free study tools. Run your draft answers through the Word Counter when you are writing up a lab report, polish the wording with our free Grammar Checker, or take a quick break with the Typing Speed Test between study sessions. Each one is free, fast, and made to keep your workflow moving.
How Punnett Square Calculator Works
Build any genetic cross in seconds, free and with no signup. Just pick your cross type, set the parent genotypes, and get the grid with both ratios right away.
Choose Your Cross Type
Select monohybrid for one trait, dihybrid for two traits, or blood type for ABO inheritance.
Set the Parent Genotypes
Pick each parent’s genotype from the dropdowns, and change the allele letters or inheritance pattern if you need to.
Build the Square
Press the button and the color coded grid fills in with every possible offspring instantly.
Read Your Ratios
See the genotype ratio, the phenotype ratio, and a short note explaining why the numbers came out that way.
Frequently Asked Questions About Punnett Square Calculator
Genetics raises a lot of fair questions, from what the ratios actually mean to whether you can really predict a baby’s eye color this way. Here are the answers people search for most, kept short and clear so you can get back to your work.
What is a Punnett square used for?
It predicts the possible genotypes and phenotypes of offspring from a cross, along with the chance of each one appearing.
What is the difference between a monohybrid and dihybrid cross?
A monohybrid cross tracks one trait on a 2 by 2 grid, while a dihybrid cross tracks two traits on a 4 by 4 grid with sixteen outcomes.
Why is the dihybrid ratio 9:3:3:1?
When both parents are heterozygous for two traits, the sixteen offshoots sort into that pattern, which shows Mendel’s law of independent assortment.
Can this calculator do blood type crosses?
Yes. The blood type mode uses the IA, IB, and i alleles and shows the possible ABO types of each child, with IA and IB acting as codominant.
Can a Punnett square predict eye color?
Only in a simplified way. Real eye color is shaped by many genes, so use the result as a learning model rather than a true prediction.
What is incomplete dominance?
It is when the heterozygote shows a blended middle trait, like a pink flower from red and white parents, which gives a 1:2:1 phenotype ratio.