Punnett Square Calculator
Cross two parents and get genotype and phenotype ratios, for one trait or two.
Genotype ratio
Phenotype ratio
Simulated offspring
About the Punnett Square Calculator
Free interactive Punnett square. Choose parent genotypes for one or two traits, see the full grid, genotype and phenotype ratios, and simulate a litter of offspring. Built for biology, the punnett square calculator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Cross two parents and get genotype and phenotype ratios, for one trait or two. Use it to explore biology ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Punnett Square Calculator
- Use the controls to change Type of cross, Parent 1: seed shape (R = round, r = wrinkled), Parent 2: seed shape, Parent 1: seed colour (Y = yellow, y = green), Parent 2: seed colour. The simulation reacts instantly.
- Pick an option such as Monohybrid, Dihybrid to switch modes or load an example.
- Press "Simulate 100 offspring" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Cross Rr × Rr and read the 3:1 ratio.
- Cross a homozygous dominant with a homozygous recessive.
- Try a dihybrid cross to see 9:3:3:1.
- Simulate 100 offspring and compare with theory.
Key ideas you can learn
- Each parent passes one allele of each gene to the offspring, chosen at random.
- A monohybrid cross Aa × Aa gives a 3:1 phenotype ratio.
- A dihybrid cross AaBb × AaBb gives the classic 9:3:3:1 ratio.
Where this is used in the real world
Genetic counsellors, plant breeders and animal breeders use Punnett squares to predict traits in offspring and to plan crosses.
Who is this simulation for?
Biology students and teachers who want to explore living systems, populations and genetics interactively and safely.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is the difference between genotype and phenotype?
Genotype is the pair of alleles an organism carries, such as Rr. Phenotype is the visible trait, such as round seeds.
What is a dihybrid cross?
A cross that follows two genes at once. Each parent makes four kinds of gametes, so the Punnett square is 4 by 4.
Is the Punnett Square Calculator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Punnett Square Calculator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.